The best time of year to plant clematis is in the spring when your vine will have ample time to establish itself before winter weather sets in. Fall is 2nd best.
Clematis prefer to grow in full sun with a bare minimum of 6 hours direct sun each day. And the more the merrier, they really cannot get too much sunlight.
Clematis like their roots to be cool and shaded. I try to plant my clematis among other flowers so the top of the vine gets plenty of full sun, yet the roots will be shaded by the other plants' foliage.