switching from Sg to a Big Man position is tough, and you'll have to be strong and big enough to make the switch. Assuming you can do the things any SG can do, your speed and Shooting ability will help you have something your opposing post players don't. Anyway, get a boz or anything heavy enough and suitable for you to make contact with and put it where you plan to practice. Do drop steps, hooks, power dribbles and anything you want to learn and make sure you make some level of contact, or have to shoot over the object you put in place. Be sure you have a strong hook and power dribble before using the object.

I am a PG, I played in the post at a young age and know what I'm doing in the post but cannot execute with taller players.

Good Luck.