i like to shift into a harder gear and build up as much momentum before the hill as possible, then try to gauge how steep the hill is going to be, then shift into a gear that fits it. the hills around here require the granny chainring and the 2nd or 3rd cog to maintain a steady pace without much wheeling, and going fast enough to not fall. i rarely need the 1st cog, thats too easy for most hills. after a bit of practice you'll be able to pre-estimate what gear you'll need. also, practice, find hills and go up them. we have short hilly inner-city hobo trails that are great for this, i just do them over and over forwards and backwards for training. if you get into speeding up on a downhill to try to get up the next uphill, watch out for mud at the bottom!