Here's a few things I use when shooting in for takedowns.
1) I shoot for a double leg takedown after the left hook. It can be after any combination of punches and the harder the punches land the better the takedown works.
A good one to start with is jab,cross,hook,double leg shot.
2) I attack my opponent's lead leg (when we are both right handed) with a single leg attack after getting in close with the jab. You may have to throw one,two or three jabs to get in close enough.
The key is to try to land some solid strikes often so that when you opponent begins to worry about your punches, you can switch it up and add in the takedowns.
Strike when they expect takedowns and take them down when they are expecting strikes.