just written you a post about this .....
Whatever you do, read everything by snYpir.
OFPEC Guide:Mission editing
Macguba's guide to mission editing for beginners (he wrote modestly)
Tutorial Mission
How to use objectives and init.sqs
then it gets harder: look briefly at all of the following and pick the ones you like to study. I'll name the authors rather than the titles, since I can remember those. They do overlap.
Devilchaser
Rob, Hangfyre & snYpir (in References)
Abuu
Johan Gustafsson (x2)
Most of the others are pretty good too, this is a very personal choice govered mostly by the ones I learnt from. (um, and wrote ....)
You should aim to produce one simple but complete mission which you can then post in the beta testing forum (don't forget to read the sticky there, also "How to make good missions" in Getting started). Having made one, you can them progress to more complex stuff knowing that you have a solid knowledge of the basics.