I started turbine transistion on the 330 9 months after I got my PPL on the 300, which puts in the summer of 1997. I have never had an issue with a start and I have a few observations that have been filed in my head. I have type ratings for 330, EC-120, B206 and H500 turbines, so my experiences are with two main engines.
Temp that's good It was said above: hot and fast is best for the engine. Fluctuations in tot and peaks are bad.
N1 acceleration It is important to introduce fuel while you still have acceleration on the N1. If you let it flat out at, say, 14% and then light off you are going to get a much more erratic start with larger peaks. Better to let go at 12% while you still have acceleration.
Battery A good battery is best. If you start with a GPU you are going to get a nice, fast start, albeit somewhat cold. I once started a 500c from a totally over-sized GPU meant for a BAE146 commercial aircraft. I wasn't fast enough to manage to open the throttle when it passed 15%... The thing was at 58% N1 in less than 3 seconds... Nice and fast
and absolutely no peaks - just a quick rise to the proper temp.
When the battery is really too low or cold I have discussed this at length with mechs and professional pilots. As we have arctic conditions here, a start at -25C or lower is nothing unusual. I was shown by a mech how to do it:
1 - If you can, pre-heat the engine some way, like with a car heater if you have electricity. It will make it spin with less friction
2 - Crank, open when acceleration of N1 decreases, even if way below 12%
3 - When tot approaches the red line, shut off until it goes down in the yellow, then open again, keep the button depressed
4 - Keep modulating off and on until you reach idle.
This may seem dangerous, but it really is safe if you stay alert and don't crank too much over the max crank time. You will not over temp the engine unless you focus on the wrong things. If it is cold, your starter will not over heat the first minute or two.
EC-120 This is one dangerous beast when it comes to battery. If the voltage drops below 17 Volts, the cut off release will not function. So, in this helicopter you have to watch the Voltage as well as the engine parameters. If voltage drops below and you get a hot start you cannot cut off fuel with the collective throttle and will have to resort to the big lever in the ceiling in order to stop the flow (naturally while still cranking with your other hand)... I wonder who designed that system.
Anyway, thoughts from an amateur with input from some professionals (and you should always listen when experience talks).