First start by using 1, 2 combinations, jab and reverse, hook punches, uppercuts to the body, low body shots(to rib areas). Use your elbows to strike the face area, use knees just like in Muay Thai, so using your hands grab the bag and knee it.
Kicks; use roundhouse kicks, do about 50 on each leg and depending on how flexible your are go either for mid level shots or head shots. Experiment by jumping, swapping stances, delvering the kicks from your lead foot or your rear foot. Try side kicks, 50 hard ones on both legs, back kicks, spinning back kicks, jump spinning back kicks, jumping side kicks, hook kicks and fron kicks.
Heres some kicking combinations you can try:
low roundhouse to calf level
roundhouse to back of thigh
high round house
low side kick
mid level side kick
hook kick to head
Midlevel front heel kick while swapping legs.
All the others you do on one leg and repeat
for the other leg so you do multiple kicks on one leg without putting the foot down.
jab, reverse, hook (alternate hands)
backfist, hook ( in one motion and alternate sides)
These are just some ideas and Ianyting else I think I would have to show you in person, but failing this just use what i have suggested and they should help give your more ideas for combos. Try using footwork, bobbing and weaving, try swinging the towards you, ducking under and using your punch combos as well as kicks. Don't stand still, strike from all angles.
I hope this has helped and if you need any more advice feel free to email me at email@example.com.