If you are having some slipping issues on the trainer, wipe the drum and tire down with some rubbing alcohol to clean it off. That often helps improve grip.
If that stops working, you can take some sandpaper to the tire to rough it up some. Sometimes tires glaze over a bit when used on the trainer a lot, and the sandpaper clears that and adds a bit more grip.
Last option, you can buy grip tape that you stick to your trainer drum, but that will chew up tires and can create a bit of a mess.