try making the start big enought for 32 players... nothing sucks more than a map with a small stair at the beginning where u cant go because everyone wants to go there too
alwasy think of idiots who just want to piss of others...
test your map before uploading, try everything, search 4 bugs and try to place the repairs at the right places
dont make the map to long 2-5 min are good
try making the map understandable, put the cps at the right place and everyone will instantly know what u want in your map
let the players do different things, a race just on the highway, avoiding barrels can get booring very quick
choose the right car for ur map bullet on an offroad track would be... eh... u can use vehicle change pickups
do something new! find something whats never been here before
dont use to many fog generators, some people got problems with the fog in gta (performance slows down)
dont make the checkpoints to small... missing a cp makes me angry^^
ah and: put funny thinks near the track, ornaments plants trees rocks... building an own small city or forest can be funny too!
i hope that will help u
greez dragon