Slow down....don't rush it. This is not a sprint...it's a marathon that takes time.
The vagina is a muscle and the only way that I am aware, I am not a physician, that you can improve your results is through a thorough "warm up and stretching routine" like any other muscle.
Don't misunderstand, what I mean is you have to be relaxed in your head, while warming up your vaginal muscle via foreplay, in order for it to perform like you hope/want it to.
Sex begins long before the actual act of penetration. With that first glance after being apart and by Kissing, hugging, holding hands, snuggling on the couch, etc. These are all types of activities that begin to prepare you for further physical intimate activity.
Once the clothes come off, spend additional time carressing, exploring and touching each other's body. Hold each other close, snuggle under the covers skin to skin. Just holding each other close and tight without clothing can be one of the most amazing feelings. Get to know your partners sensitive to the touch spots, he has many more than the obvious ones, and let him get to know yours. Use your eyes, fingers, lips, tongue and sense of smell to take it all in...then allow it to sink into your mind as to just how amazing all of this is, before you move on to the next stage.
Physical intimacy is the most amazing gift two people can share with one another. So be patient and take your time to discover, explore and learn those things that "turn him on" because, in part, doing so will turn you on, warm you up and help your body relax/prepare for what's to come.