Amend your soil so that it drains well and has lots of nutrients. Water regularly but not heavily. Try the viticellas or montanas. They're pretty hardy and easy-care. Keep the roots cool with mulch or a stone, anything to keep direct sun off them.

Keep trying. I failed several times with clems because I didn't follow the points I listed. Since I've implemented these changes, they're thriving.

Good luck to you!

Suze

What size are you buying? You might have better luck with a well established one from a good nursery? Those little ones the box stores sell are a waste of money.

A little more info...when planting, add a little bone meal in the bottom of the hole, maybe 1/3-1/2 cup. Plant your clematis deep enough so that about three inches of the vines are also buried. Water is very important...water it in well so the soil settles in well around those roots. I push the wet earth down with my hands to squeeze out air pockets but don't compact it down so once the soil dries a bit the poor clematis is like it's trying to grow out of a brick. I would definitely try the group threes or the montanas. Clematis need a little care. It doesn't hurt to trim them back a little once you've planted them. Don't fertilize that first year. The roots need to become strong and don't need competition from the top growth that first season in your garden. In the early spring fertilize with tomato fertilizer. Pruning group 3s can be cut down to 4-6" at that time. Once you find out you can do well with group 3s you might then try the pruning group IIs. Look for books online about clematis. You can find them used or new. I've bought them used and they're just like new and there's a BIG savings.
P.S. rinse that planting medium off your new plant...as much as you can. I just use the hose.
Tanya