A HELPING HAND
One of the more exciting things to do to your jackoff friend is give them a handjob. By this point you've probably already established whether this is something you're both interested in, but approach them respectfully regardless. Compliment their penis and ask them if you can touch it.
If they agree, be gentle and take your time. Get yourself in a good position - sit closer to them, remove their pants if they're in the way, maybe ask them to spread their legs and move to the floor so you have better access. Both of you should be as comfortable as possible.
Make sure to get plenty of feedback - would they like more lube, are you going too fast, which part should you focus on. And most importantly - remember to have fun. The goal of this isn't to pump their balls empty as soon as possible, it's for the both of you to enjoy yourselves.