Eaglefire, to make a good gunner, first you need to do is to find a good base stat and with same ability gunner, i.e. +11 acc/ +11reload (if you're new in this game, you already have +10acc/+10 reload and both with 30 ability)
Get as much experts as you can during battle, once they got over 100 experts, then you can start 'burn' them and creat vet. Everytime, only 'burn' 30 to max 40 experts for vet, otherwise, you may end up loseing all experts.
Please forget cloudclear's suggestion as AB-ing in this game will receive Ban account in this server. Detail please read here: http://trainworld.us/NF2/English/warning.html

Airstriker... I guess you mean fighter, bomber.. etc. Same as gunner but you need to find the sailor which have more growth on plane, bomber and fighter

there is a way allowed in Chinese server,but I am not sure if it is allowed in this server.....you can use AB way to make your sailor`s level growing up quickly. But first of all you have to find some good 1 level sailor .