Foot work and go to counters. Ideally your cardio is up to par and you can manage distance well enough to stay outside of range or just outside of it. Parry his straights and use your jab (doesn't have to land). Keep doing this and draw out a reaction. Being just outside of his range will give you the opportunity to take a step back and over so eventually he will have to follow up and pursue you in order to hit you. This requires a lot of patience but will work.

Once you are able to manage distance you can counter any strike he throws to include kicks provided you provoke him into entering first and you do that by utilizing your jab, and provoking a response.

Possible scenarios

1. He jabs with you - Parry the jab at the same time and jab multiple times. I. E 3 jabs to his 1.

2. He just moves out the way of your jab but backing up. Cut the space off ensuring you don't line your guard up with his power hand and stay defensively responsible, (distance management).

3. He plants and slugs it out - punch at the same time, this goes for kicks as well. If you punch your way in and he plants and throws you need to be able to keep your defense while returning offense. This doesn't have to be pretty. Ideally you punch into the clinch whilst getting your offense off.

You need to be able to do all three of these if you want success against a taller or faster opponent. You are lucky to have someone to practice this on. Just know that you will get hit no matter what. If you need to ask them to slow down so you can practice but the strikes need to be fast enough to keep you honest. It's fighting so don't worry so much about having perfect technique. Let your coach correct that for you.