The magnitude of the ramp kind of depends on how many decks you're playing. for instance, if you're playing single deck, you'll have a small spread, and may merely add a chip with each increment in the count. But if you're in an 8D shoe, you might be going in with much bigger increases at each TC.
One simplistic rule of thumb (that I liked for its simplisticness) is to assume that each TC + is worth 0.5% advantage. So, for each step up in TC, bet an additional 0.5% of your bankroll. Remember that TC +1 may be zero edge, depending on the house edge of the game you're playing.
For instance, assume $10,000 bankroll:
+5: 200
+4: 150
+3: 100
+2: 50
+1: 25
0 -: as little as you can get away with.
My own personal ramp is even more simplistic, because I use an unbalanced count, and because I'm lazy. I just set my max bet at a fairly arbitrary level compared to my bankroll (under 1%), then "fit" in some sort of bet ramp to the running count that seems natural given the game I'm going to play.