The temptation to put your high gear cost tanks first is pretty high, because when else do you have 10 gears all at once unless the battle is already won? But you should resist this temptation...my first row tanks (all mediums for sufficient firepower/survivability balance) are all 4 gear cost except for one 3 gear cost. THAT is what gets the deathball rolling. The first enemy tank is greeted by three of my tanks, so they don't have to take much damage at all.

I suppose the lone exception would be to have Maus or another tank with invulnerability to bulwark your lines while you establish the deathball...but I don't own any of those so I don't know much about them except what I see from the other side of the gunsight. Actually, I just shelved the T30 Nira I had been working on in favor of the Catriona I just researched (so glad I didn't research the last one in the lab)...she's going to be a much better contributor once I get her leveled up some.