Yeah Kerensky that was suggested already heh
Well what I normally do is put two or three tankers per four warships and in the preshield and pre-armor eras I tend to have two or three supply pods per warship.
The important thing to remember is that you shouldn't over extend yourself, watch how far you penetrate into enemy lines before you get troop ships, because until a colony ship arrives and plants a supply base for you your out of luck if the enemy attacks you using attrition warfare.
It's actually cost me wars that way where i have no choice but to offer the AI a major something or other to get them to accept peace for a little while.
I once lost a 35 ship fleet (which at the time was the bulk of my navy) because I lost my supply ships and didn't realize I lost ALL of them until it was too late. And then it was just a matter of being whittled down until my last 20 ships had no supplies and were damaged, lol I think the AI finished them off with three destroyers.