Play the Defrag rocketjump map, I think it's called Tow1f.
I features high rocketjumps and rocketclimbs.
Also play that original Q3 map that has the BFG obtainable via a bouncepad which you need to rocketjump up to. Having a goal like that can help motivate you.
Mainly just the Tow1f though.
There are more advanced jumps like rocketjumping sideways or strafejumping into a rocketjump, which you might learn easier if you watch other players do it, from their point of view.
Basically, thiough, learn how to do Tow1f (there are demos to download if you are stuck), learn strafejumping on Defrag asell (the one where you keep jumping over lava seems fine to me), and try to put the two together on some regular maps.
Maybe I should explain a bit more: By "strafejumping into a jump" I mean you strafejump then you do a rocketjump without stopping and standing still. It's basically a running rocketjump except it's strafejumping and rocketjumping instead of just running and rocketjumping. You carry the momentum forwards so you go further aswell as higher.
Actually that reminds me there are some Defrag maps where you have to go high and far with rocketjumps; well to go extra far, in my experience you have to rocketjump backwards - though you can change direction mid air, so long as you do it so that it doesn't interfere with your air control or momentum. Pretty hard I know but that's Defrag for you, it pushes your limits.
There's a lot to be said for just practicing on regular maps, though, cause then you learn jumps that will help your gameplay in battle rather than just Defrag runs - they are good at boosting your skill though. like I said.
I was going to post a link to Defrag but the one in my bookmarks is broken. I'm sure you can find it, though
