G'Day,
It would depend on what type of finish you want to achieve with the camo scheme.
If wanted soft edges,
http://www.cobraleader.ath.cx/models/image.../gal_il2_04.jpg
I would recommend an airbrush with low air pressure and "draw and fill in" the camo scheme - may take awhile to paint the entire model, but the results are worth it.
If you want a hard edge to the paint job, like
http://www.cobraleader.ath.cx/models/image..._spitfire07.jpg
then use masks, like tamiya tape, silly putty, liquid mask with the airbrush. The use of these will depend on the type of camo scheme your doing - splinter or SEA, etc.
If you go for soft edge scheme, use a soft pencil - not lead pencils as they show up through the paint job (well the ones i've used have), that way you can markout where you want your scheme. I put a dot of the paint I want in that area so that I know I won't stuff up - especially on complex patterns.
If you do "stuff up" re-apply the base coat and start again.
Anyway, have fun with it.
Cheers
Mark