Not that I actually follow this tip much anymore, but it’s invaluable for the new stitcher, or the first few times you move from aida to evenweaves or linen. If I think that my fabric might not be big enough for the design I plan to stitch, I do grid, just for safety. There is nothing more frustrating than getting near to the end of a project and realising that you haven’t left enough room for framing – cushions perhaps? – and the start point/centre points can be super critical.
This is from Liz the StitchSmith’s site. She ran the embroidery course I went to last year (that feels odd to write that, last year!) and she’s fantastic. http://www.thestitchsmith.co.nz/
Grid marking:
I find it helpful to mark a grid on your fabric so it’s easy to keep track of where you are. You can do this on white Aida with a water soluble marker pen – just draw your grid on and then once you’ve stitched the design, it washes right out.
With black Aida though you will need to stitch your grid. This is easy to do and worth taking a few minutes extra time. Just take a single thread of your stranded cotton and make large stitches over a 10 block square as shown in the photo. Download pdf to see a bigger image.
Once you’ve done one row it’s easy to do the next rows – do make sure your first row is correct!
When you are stitching try not to pierce your grid thread as this makes it just a bit harder to pull out when you’ve finished. It also leaves behind a bit of fluff. If you do find this happens, just wrap some sellotape around your fingers and dab away the fluff. Easy peasy.
On your chart, you will find it helpful to rule the 10 block squares in a highlighter. These squares will match the gird on your fabric. Mark off the rows as you go so you don’t keep having to double check where you are.
sewscrapmuse 
Just be careful. There are some well known brands of water (and air) soluble markers that will actually rot the fabric. The disaster is speeded up by the sun….
The pen I’ve used is the one from Liz
I don’t know what make that is – but I refuse to sell any of them any more. I’ve seen some terrible disasters with the ‘very safe’ one. I only use stitch if I want to mark – sadly short cuts often aren’t in the long run.
there’s a plastic thread that can be used for gridding your fabric, I used to use it when I was working on big projects like the Dimensions kits. it doesn’t leave fluff and can be used again, it’s also very easy to avoid when stitching 😉 it’s called Easy Count Guide Line, and you can see it in some of the pictures in my gallery, look for Kitty Litter in my blog 🙂
Personally I don’t grid (I did once, but I’m so careful (read: OCD) about counting that I don’t bother) but some people use fishing line to grid with.