I hold the throttle just below the gear change indicator at the start while on the grid, then as the lights go green I change into first and gently squeeze the throttle to full gas. This generally gives me a good getaway, depending on the setup.
After this I hold the line as much as possible, it's a good idea not to cross lanes a lot at the start, although I might make some corrections depending on what's happening around me. If I'm on the inside at T1 I'll take the inside line, if I'm on the outside I'll go round the outside. I don't try and muscle my way to specific position, as it just causes accidents 75% of the time.
When coming into T1, if I'm at the front of the grid I'll go aggressive and brake hard and late, try to put some moves on the guys in front. If I'm in the middle of the grid then I am very cautious, I brake gently and often just let the car idle into the first bend. I watch my mirrors carefully and if I see anyone too hot behind me then I'll take avoiding action. If I'm at the back of the pack, then I just take my time, I hold back and let the carnage in front just play out by itself, which will net you four or five places usually, on a packed grid.