All the tips here are very good

- weight shifted forward - you may even need to move around a bit to ensure traction on both wheels
- easier gear
- BREATHE! its amazing how many people forget
- patience! nothing aggravates me more than to see people try to "momentum" up a hill in too hard a gear, at an intensity way past their fitness levels. Just be patient, the top of the hill will be there faster than you think. I have passed people who blew up before the top, because they tried to speed up the hill like that.
- riser bars tend to make climbing more difficult as it sits you more upright
- saddle position - make sure it isn't tipping "backwards" because it too will make sliding forward more difficult
- and overall geometry of the bike - all mountain bikes versus a cross country designs - even overly small frames like mine, affect the ability to shift forward and effectively transfer weight and traction to the front tire.

Happy Climbing!