For general cross stitch tips and tricks - download pdf
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.