"My new boyfriend has a smaller penis. How can I make sex more enjoyable?"
I think the first thing that's important here is how to define 'sex.' Remember that not all sex has to be vaginal intercourse. If you don't feel as much pleasure vaginally, try doing more oral, manual, or mutual masturbation. Also, it's not how big it is, it's how you use it. Focus on touching and stimulating every part of each others bodies--the sex doesn't have to be the biggest part. But there are positions that can make a guy seem long and penetrate deeper.
Doggie Style--Doggie style tends to rub against women's g-spots, since it is only a few inches in on the upper part of the vaginal canal. Because of the position (woman on all fours, head down, man in from behind), the penis will feel like it is penetrating quite deep.
'Rabbit Ears'--Have the woman lay on her back with her legs bent up towards her head and enter from the front. The angle at which the penis enters, combined with her holding herself in a condensed position, will make her feel like you are all the way in her.
Legs Together--Any position where the girl is either on top or bottom (preferably bottom) and she keeps her legs tight and together will make the penis feel like it has to struggle to get in, and it will feel that it fills deeper.
Also, don't be ashamed to accept help! Man on top positions are great because even if he is small, this position causes the clitoris to be rubbed, enhancing pleasure for you. Vibrators and other sex toys are great to add in as well, either for external or internal stimulation. Remember too that there are 'growers' and 'show-ers.' Your guy might look small, but when he's at his sexual peak, he may be totally average. Again, it's not the size, it's how you use it.
Cosmopolitan--Small Penis Positions-Advice