Short way to say it -
Find a hill that's pretty easy to climb & just keep riding it daily. Once you start getting used to it & can climb up easily, start attacking from bottom to top w/ a larger gear & time yourself every time. Know your limit !

What helps -
hands on top of the bars
relax upper body, too much movement can tire you out
which method helped me (just got used to it after) = keep your heels down while pedaling
& the biggest one, stay seated

Goodluck !