As Neil Kurzman stated - avoid the pitfals. There are not too many of them. They have been already listed: use the smallest type you need (uchar, avoid float), break up your code to small units (the compiler might easier keep track of which variables are needed and does not need to move them around unnecessarily). Avoid printf and similar "multiuse" "universal" library functions, they are unnecessarily inflated.

As for the rest, how much do you expect to spare? If it is less than say 30-40% - and I'd bet it would be FAR less - it was not worth the inconvenience of thinking on optimisation all the time.

My 0.02 SKK (practically zero)

JW (the C-hater)