If you are using one of the 3.5" semi auto's, you might want to stick initially with a 1 1/8 oz. lead load. Some 1oz. loads will cycle some of them, but not others. If you shoot a 3" semi auto, most of them will cycle the 1 oz.loads well, however they may need to be close to 1300 fps. to do so. The Italian and Browning gas operated semi autos function more reliably with 1 oz. loads than do the Rem. 1100 or 11-87.
I like fast moving loads and use International Clays and some other powders which will give me 1345 fps, or faster, loads with 1 oz. of shot. Any of the Hodgdon Clays powders will burn very cleanly.
I would suggest you have an experienced loader help you starting out. Loading is not particularly difficult, but there are a few tricks involved that can make the process easier. Also, ask some experienced sporting clays shooters for help, as they will usually shoot in cold weather. Trap and skeet shooters usually give it up when the temps drop. Often, low pressure loads that work well in warm weather, don't work so well when it gets cold. (Ask Jon Brunner about that one.<img src="/images/boards/smilies/biggrin.gif" border="0" align="absmiddle">. I had to loan him some shells for his first shot, so his Xtrema would cycle last weekend.)