Well, I usually make two groups. Parts that are the main body color (single or camo) and parts that are not (accessories). I glue together most of the parts.
Such as for example I am doing a Sherman now. For the lower hull I constructed the lower hull except for maybe two parts. The turret is mostly constructed except for the 50 cal.
The upper body has most except accesories. If your doing a tank with zimmerit then you should apply zimmerit then apply, but note zimmerit is applied by the tank crews, so apply the detailed peices like handles etc.to the tanks upper hull as if the zimmerit was put around it.
go to http://members.ozemail.com.au/~firestorm1/How%20To/zimmerit.htm for zimerit stuff.
Back to the sherman. Then, I airbrush the OD green and any other colors (i did white for a winter camo too, undercoat of black and brown to make weathering and darkend paint appear under the green), becasue everything i have constructed is OD excpet for het wheels and gun barrel on the hull, which i paint later.
Then I glue the upper hull, lower hull and turret together. I paint my wheels and gun barrel and anything else small on the tank which is not OD green. Now comes the acesories. I handpaint them, but I use a toothpick to apply the glue as not to mess up my paintjob (some and most glue is corrosive to paints, even if you wait a day).
After all of this, you should have all done save the figures and tracks. Do the tracks with you weathering technique, however you prefer. Apply the tracks and figures. Your Done! I didnt write the time you wait during painting, but Im sure you know that you wait about 24 - 48 hours in between coats.
Basics (in between my ranting), paint all of the same color things together after gluing them. Thats all.