i had this very same problem when i began riding my bicycle again. coming from the midwest to a mountainous region presented a lot of new challenges for me, climbing being the one i struggled with most. after consulting Ned Overend's Mountain Bike Like a Champion and the board here, i learned a few things. Sliding up to the front of your saddle will do wonders! It might not be the most comfortable, but getting to the front of your saddle will really make a difference in how you climb. i also started using barends, which might not really improve anything, but made climbing more comfortable and managable for me. and last but not least, don't be afraid to lay over your bars on the real steep sections. Having your chest an inch or two above your bars effectively shifts your center of gravity, applies more pressure on your back tire which will give you better traction, and will really help you keep your momentum which inturn will prevent you from toppling over on the steep climbs. Keeping your momentum while going into an uphill always makes it way easier to climb and willl help you work on better shifting. Momentum is key when you have a lot of up down kinda climbing. find you flow, happy trails, and even longer climbs to you friend!