Assuming you've looked at the range and speed of all of his normals first...
Start by throwing slow fireballs at the training mode dummy. Then moderately fast fireballs and then the fast ones. What you're aiming for here with this exercise is to try and be able to throw fireballs endlessly without getting an accidental back, forward or neutral punch. When charging you always want to be holding down+back (db) because that means you can charge your Flash Kick AND your Sonic Boom.
Charging tip: When using charge specials you can charge by holding db then rapidly moving to forward then again to db but this time you press db+attack button. So for Sonic Boom it's B,F, B+Punch. This allows you to throw the fireball but start charging instantly, like as soon as the fireball is thrown you're charging from frame 1. This is useful because if you go to db and charge instantly, you can FK people who are trying to jump Booms on reaction and inevitably failing lol.
Another warmup/exercise you can do is whiff (or hit) LK Flash Kick and then as soon as you land do another one. If you can do that then you're charging pretty well.
As for combos, just start off easy. Do the trials and learn the links.
-Learn the punish for failed DP's. CC F+HP, dash, HP, cr.MP xx Ender/whatever vtrigger stuff you want to do.
-You want to practice the MP, cr.MP xx Ender combo
-Your light hitconfirm/crossup combos. cr.LK/LP, cr.lp xx Flash Kick
-Don't worry about the loops in the corner just yet. You can start off with a BnB like HP, cr.MP xx boom xx Trigger, dash, HP, cr.MP xx Flash Kick then save vtrigger for pressure or whatever you want.
If you're trying your hardest to throw somebody but they're so damn good at teching then don't worry Guile has a safe option to deal with that too. F+HK, the Upside Down Kick. It's airbourne so it's throw immune and therefore anybody trying to delay tech will get caught by this and eat double the amount of damage they would have taken for getting thrown. The combo is UDK, cr.MP xx Ender/vtrigger if you want to.
Guiles a simple character and once you learn how to charge and it's second nature you'll find out just how easy it is to use him. Nothing complicated, just, getting to chuck plasma and poke people all day really. I'm sure you won't need help with his V-Skill, it's pretty straightforward and an excellent tool.
That's my tips, I'm no pro or a great player or anything like that but I have a graps on the game I'd say and I know what's happening. Good luck!
