tl;dr all the crap above

1) Do hill repeat workouts. Do some in difficult gears, do some in your easiest gears. Seated and standing. Kill yourself.

2) Let yourself hurt a little. Hills are hard. They're supposed to be. Flats are easy. They're supposed to be. So if you're cruising along at 24 or whatever on the flats with relative ease...don't hold that same effort level on the hills, cuz you'll get dropped. No...you have to hurt on the hills. Then you can cruise again at 24 on the flat to recover a bit.

3) Carry momentum into the hills. If you know a hill is coming, pushing on the flats where it's still easy so as to carry more momentum into the hill can pay dividends.

4) Make sure you learn to shift at the right time, into the right gear for your you. There's a fine line between pushing too hard, not pushing hard enough, and the shifting at the right times to continue on that fine line instead of getting derailed.

5) Also...if you know a hill is coming and you're in a group...well, suck wheel for a while before the hills! That might give you just enough energy saved to not get dropped by those guys that climb better than you.

6) Every bit of resistance saved helps. Get lighter (you and your gear), especially lighter wheels. Get low crr tires. Get aero frame/wheels.

7) Maybe get a wider cassette? You might need a 26, 27, 28...and just spin like a banshee to keep up.