Well I'm tall and lanky (not that tall, about 5' 11 1/2" almost 6'), so I like to stick with straight punches and moving in and out of range, like an Outside fighter) or allowing the opponent to come to me (back when I sparred a lot, I would parry and counter). The combos that I found that worked best are the simpliest ones, it took me a while to figure out, but any combo that is more than 4 punches in length will usually fail, especially if they are complex (like Jab, Cross, Left Body Hook, Right Hook, Left Uppercut, Cross- who is going to remember all of that? Really!) So I will give you the combinations I use, and notice, to be success with my style of combination, you have to move in with your punches, simply standing in stance with these punches will leave you open for counters.

Jab (move in), Cross

Note: (An exception to this is someone coming in with straight punches, you can parry and unload a 1-2 of your own, wouldn't suggest it though)

Jab (move in), Jab, Cross

Jab (move in), Cross, Left Head Hook, Cross

Note: Defense is very important on this combination, especially on the Cross, because your opponent can unleash a Left Hook if you're not careful enough. I personally find this combo works best on shorter opponents, for taller opponents, I suggest throwing the Left Hook to the body and Cross to the head)

[Inside Fighting] Right Uppercut, Left Head Hook, Cross

Note: This works especially well against opponents who move in and start punching to the body, they never see it coming)

So in review, you really only need to know about 3 combinations:

Jab (move-in), Cross (the other varation being Jab-Jab-Cross)

Jab (move-in), Cross, Left Head Hook, Cross

Jab (move-in), Left Head Hook, Cross

The Inside Fighting combo only needs to be used on the Inside, but the other three combos should help you out.

If you like, I can email you my personal notes, which you can read and print off to use either in sparring, or hitting the heavy bag. Good luck!