When I give my boyfriend a handjob, my wrist always gets tired long before I can get him off. See, he likes it really fast, so I tire quickly and end up feeling like I failed. He's a really good sport about it, and "helps me out" while I rest my arm a little (usually he gets me to start again when he's close), but I'd still like to know if there's anything I can do to get better at it?
(Heather will most likely groan at the subject title--bear with me, I'm old and find humor in puns.)
Of all the sexual proclivities I enjoy, a handjob is not one of them. Like you, my wrist will give before the guy will come. I'm good for a few minutes, but after a while I say to myself "Oh COME ON already!" It's not the guy's fault that he takes a while to come, we simply don't have the endurance in our forearms that they may have developed. Are there solutions to our problem? You bet!
The first thing you should do is ask your boyfriend what he enjoys. You can start the conversation by saying "I like it when we're together sexually, and I really want to enjoy what I'm doing. What are some things you like that I do, and what are some other techniques that you'd like me to try?" Initiating a conversation will allow you both to talk openly and honestly which is super-important for a relationship. You may also learn that he might prefer a drop or two of lubrication when you're stroking him. Or that he doesn't like it when you move your hand from the head of his penis to the base of his shaft: he would instead prefer you to focus on the head using rapid motion. Maybe he'd like you to try using your other hand on his scrotum and gently massage him while stroking with your other hand. Once you two talk about what he likes, and what you're willing to do, you two can reach a level of comfort and patience that's enjoyable for you both.
You'll also want to add some strength in your forearms, and this can be accomplished with simple yoga postures or practicing with meditation balls in the palm of your hand. I really recommend the yoga, it will give you strength and endurance with the added benefit of giving him a better handjob.