Your cover is your most effective marketing and sales collateral for your book. People do judge books by the cover, so it's important to get it right.

What follows are some tips on the mechanics of laying out your cover. But it's not a course in graphic design: you're still going to need some visual flair to put together a great cover. If you don't think you have the necessary visual abilities, find someone who has. Design is a skill - it's not something you can pick up overnight.

This article uses Photoshop and InDesign as the file creation tools - because they're the best tools for the job and because that's what I use. But the steps outlined here will transfer equally well to other DTP or image editing software.

For the sake of this article, let's assume you're producing a 6x9in perfect-bound trade paperback. We'll also assume that you're designing a one-piece cover that incorporates front and back covers plus spine - although much of what you read here will be just as useful if you're creating separate images for front and back.

Before you can start, you need to know the width of the spine. This depends on the number of pages in your book and the type of paper you're using. Your printer or POD service will advise you. Lulu, for example, has a calculator for this (look under 'Creator tools' in the sidebar when you're logged in to your dashboard). Although you can always tweak your design later, should the number of pages or paper stock change, it's a lot easier if those elements are fixed before you start. So lay out, proofread and finalise the book contents before starting on the cover.

Image size and bleed area

If you're book is 6x9in you might assume you need a 6x9in image for the cover. Not so.

Printers require a 'bleed' area around the cover image. In effect, this allows a margin of error when the printer trims the book. Any image or text that extends all the way to the edge of the cover should continue into and right to the edge of this bleed area. If you end the image at the edge of the main page, you risk having a white border appear when the cut doesn't quite match the edge of the image.

Lulu specificies a bleed area that extends 0.125in (0.36cm) beyond each edge. This is a typical figure used by many printers. For example, with a book height of 9in, the height of the image needs to be 9.25in, and you should assume that the top 0.125in and bottom 0.125in will get trimmed off.

For a one-piece cover, the image width needs to be twice the width of the book, plus the width of the spine, plus a bleed area each side. Let's say your 6x9in trade paperback has a 1in spine: the width of the image will need to be:

0.125in (bleed) + 6in (back cover) + 1in (spine) + 6in (front cover) + 0.125in (bleed) = 13.25in

So, for this example book, the full image size is 13.25in wide x 9.25in high.

Don't make the bleed area any bigger, "just to be on the safe side". Lulu, for example, assumes that the bleed area will be a fixed 0.125in: if you make it bigger, Lulu will rescale the whole image.

Lulu also suggests using safety margins inside the main (6x9in) page area of 0.25in all round. You should keep any text or images that you don't want to bleed within these margins to avoid any danger of them getting trimmed. (That margin width is just for covers - Lulu suggests 0.5in for inside pages).

Let's look at setting up the image in two separate programs - Photoshop and InDesign.

Using InDesign

I prefer InDesign because it's a page layout program and what we're doing is laying out pages. Well, duh.

Start a new document. Select 'Custom' in the 'Page Size' option, number of pages 1 and make sure 'Facing Pages' and 'Master Text Frame' are unticked. Now we need to enter various dimensions.

The width you enter should be twice the page width plus the spine - don't include the bleed area. In our example, this width is: 6in + 1in + 6in = 13in. Similarly, the page height should be 9in (ie, without the bleed). Why? Because, being a proper page layout program, InDesign knows about bleed and allows you to specify that separately. We'll come to that in a moment.

Being old school, I like to work in picas, so that's how I have InDesign configured. Fortunately, InDesign allows you to enter measurements in any unit you like and automatically converts. So I typed '13in' into the width and '9in' into the height, which ID converted to 78p0 and 54p0 respectively.

I set columns to 1 and ignored the gutter setting as it's irrelevant.

I then set the margins to 1p6 - which is the same as 0.25in - our safety margin. And I set the bleed area to 0p9, which is 0.125in. We're all set.

Once the blank page comes up, I set vertical guides at the 6in and 7in points, marking the spine. This gives me a blank page that looks like this:

The outer, red frame marks the bleed area. Any image that needs to bleed off the edge of the page should extend right up to this line.

The black rectangle marks the actual page size. The inner magenta line marks our 'safe margin' - we're going to keep all important elements inside this line.

The two vertical cyan lines mark the spine. For the sake of symmetry, you'd probably also want to add two further vertical guides, 0.25in either side of the spine guides, matching the margin on the opposite sides of the pages. These two guides would be at 5.75in and 7.25in.

Let's put an image in there. I have a cover image I created (in Photoshop) for my novel Lady Caine. Here's what the layout looks like with the front cover done.

There are several things to note here.

First, see how the text for the title etc is nicely inside the magenta safety margin. It's well away from the page edge so there's no danger of it getting trimmed or even looking crowded.

At the bottom of the page, the black area needs to bleed off the page, so it extends all the way beyond the page limit (the black line) to the full extent of the bleed area. (In this image, the blue frame of the image is covering the red line denoting the bleed area).

The aircraft's wingtip is coming quite close to the edge of the page, but I was happy with that because it doesn't really matter if it gets trimmed a little.

So you can see more easily what's happening here, let's look at it in close up. Note how the black area crosses the black line of the page boundary and extends out.

The left-hand edge of the image ends abruptly at the spine. This is a little dangerous. Slight variations in trimming can mean that the spine might 'bleed' slightly on to the front cover, or vice versa. Having such abrupt changes at the spine boundary is, therefore, not generally recommended. In the case of this book, I did this because, in fact, the cover design was not done as a one-piece. If I had designed it as a one-piece, I'd have extended the graphic over the spine and even on to the back cover.

Lulu asks that you supply one-piece covers as PDFs - indeed, that's typical of many POD services. I'll be blogging separately about PDF settings and options, but there's one thing we need to cover here.

When outputting to PDF, make sure you include the bleed area in the PDF file. When you come to export as Adobe PDF, the (somewhat complicated) PDF options dialogue includes a page for 'Marks and Bleeds'. Make sure the 'Use Document Bleed Settings' is ticked. (However, under 'Marks', do not tick 'Bleed marks' - most POD publishers do not want these included).

Using Photoshop

Things are slightly trickier when using Photoshop (or another image editing tool) just because it doesn't offer bleed and margin settings, so you need to do a little more work with guides.

So, here we are creating the new file:

A key thing to note here is the image size. This time, because Photoshop doesn't have a separate setting for the bleed area, we're creating an image with the bleed area included - 13.25in x 9.25in. I've gone for 300dpi. You may also notice that I've opted for sRGB as the colour space, rather than Adobe RGB. The latter may work with some POD services, but the more limited colour space of sRGB is probably safer.

This creates a blank image. Now we need to add guides. The edge of the image denotes the bleed area. We want both vertical and horizontal guides 0.125in inside the outer edges to mark the limits of the pages. And we want other guides 0.25in inside those to mark the 'safe margins'. In addition, we need two vertical guides to mark the spine - and another two vertical guides either side of the spine guides, and 0.25in away from them, to complete our safe margin guides.

Let's start with the vertical guides. The first is at 0.125in, marking the edge of the page inside the bleed area. The next is at 0.375in - that's 0.125in for the bleed + 0.25in for the safe margin.

Next, we'll mark the spine, because it's easy to calculate. The left side of the spine comes 6in from the page edge. The guide that marked the page edge was set at 0.125in. Therefore the spine starts at 0.125in + 6in = 6.125in. Our spine is 1in wide, so the other guide needs to be at 7.125in.

Now we want to add the guides to mark the safe margin either side of the spine. The one for the left side (the back cover) needs to be 0.25in inside the spine guide - ie, 6.125in - 0.25in = 5.875in. The guide the other side (for the front cover) needs to be at 7.125in + 0.25in = 7.375in.

Remember that the right-hand page (the front cover) started at 7.125in, which means the right-hand edge of the page must be at 7.125in + 6in = 13.125in. (Or, you could have calculated this from the width of our whole image, 13.25in minus the bleed area width of 0.125in.) And we need a safe margin guide inside that: 13.125in - 0.25in = 12.875in.

Now you need the horizontal guides. There are only four of them, marking the page edges and safe margins at 0.125in, 0.375in, 8.875in and 9.125in.

Here's what the image looks like. To highlight the different areas, I've tinted the bleed and safe margins. The grey area around the cover is Photoshop's pasteboard and doesn't form part of the image, but it does show you where the guides are. The red areas are the bleed, and will get trimmed. The beige areas are the safety margins. They will form part of the cover image. The white rectangles are where it's safe to put text etc.

You wouldn't want to actually have these red and beige tints in your image - I've put them in purely for demo purposes.

Once you've done all your design work, you're going to want to output as PDF. Select 'Save as...' and choose the Photoshop PDF format.