[woodcote]

Some wider radius turns should probably be on your shopping list - you'll be able to run the cars a little faster into (and out of) the corners and you can build some 'compound' corners as crustypop suggested. That makes the layout more varied and interesting.

If you're using the fuel simulation on the Digital Control Unit (or in the app), then a pit lane will make things much more realistic.

More lane changers too 

You might also find you need some outer borders on some of the corners so you can drift the cars out.

Have fun