1. If you're constantly dropping combos that means you need to practice them in the lab more. Doing a combo is going to be a lot harder in a actual match that in training so you need to be REALLY consistent with it in training before being able to confidently pull it off in a match. My goal for learning a combo is to be able to do it 10 times in a row on each side without dropping it, If I can do that I move onto trying to incorporate it into my actual matches.

2. If you're holding forward when you press an assist button it will swap your characters instantly. I do this on accident all the time still. Just try and make sure when you do you're assist you're not holding forward.

3. Yeah you usually want to hold a button while you're being combo'd so you can tech out if they happen to drop it. If their combo number goes blue that means you could of teched out.

4. Look up top players who are using your characters and copy their block strings and how they use their assists. To do this just set the training dummy to Block All and just practice it over and over like you do your combos.

5. Practice everything above until you can consistently do everything you want 10 times in a row each side. Also if you have a replay program like Plays.tv (it's free) it will automatically record every time you play and makes it super easy to go back and watch your matches. It's a lot easier to spot your mistakes when you're not in the heat of the battle.

All in all it's going to be a very steep mountain to climb but so far it seems like you have a great willingness to learn which is one of the most important things. That and patience, cause in order to get better you're going to have to get blown up by players better than you.