There are several things you can do.
Let us begin with your counterpart, your top. A good one shall provide you with various forms of foreplay. This will help you relax before you and him...hunch. (I pulled that term out the old school country dictionary). Depending on what type of person you are, certain types of foreplay will be much better than others. Foreplay is necessary to maintain heighten senses, increase the blood flow along with the heart rate, and relax the body.
This can turn into a whole other topic, but since no one has responded in days, I'll go.
Lets start with smell. Every man has a certain smell that is released when they become lustful i.e. horny. (I feel so filthy using these words)
Anyway, the pheromones, have a chemical substance that attracts their partner.
Next, you two will touch each other. I find that touching palms to palms (Nerve endings), while gently kissing on the lips is a good start. Next, (listen up tops this is important) your top should gently glide his hand and arm around your waist, stopping at the small of your back while at the same time, pulling you closer to him. You are going to feel his identifier, and it will be much larger and harder than you remember, don't buckle. (Tops, you're welcome.)
Bottoms. When this happens you are submitting to your top. This means you are non-verbally allowing him access to explore your body, and instilling trust in him. (If your mind is not willing to allow this trust threshold to be crossed, then something isn't right, and stop.)
Your top will typically be in the drivers seat so, he should be kissing, or lightly biting you in all the right erogenous zones. (You know, lips, hips, earlobes, collarbone, pecs). It's okay to return the favor to him.
Next is sound. I got to be honest, because I'm a verbal person, this step will make my knees buckle. (That's why it's important to have a trusted top to catch you as you melt in his arms). His voice, will drop at least two octaves into a baritone so low, that when he whispers in your ear, it will send vibrations to parts of your body you didn't know had nerves.
He will say all kinds of things from, how hot he is, to how good you look, to how you make him feel, to how good you feel in his arms, to how he wants to make you feel.
He will ask you things. If your response is anything like mine, you won't be able to say much. You'll do one of two things, moan or whimper. Hell, it doesn't matter by this time you'll be putty in hands.
Cleanliness, is next to godliness. Make sure your mouth, and entire body is clean before you start invading your partners space. (I understand, that some men have fetishes that are pure mud, if so, please ignore.)
Last on the list, is taste. I hope I don't have to give too much detail, but I will say, quiet as it's kept, your top prefers a certain flavor so...light his palate up. Think of it this way; your body is a three course meal, complete with a drink
. Your man will need, spicy, savory, and above all, sweet.
If all of those options are available to him, he will make sure you will be ready when it's time. After a while, you'll get use to it, and you'll be riding it, like Scarlett O'Hara rode that horse back to Tara.
Don't be a fool, keep it wet, and if he doesn't have a glove, then he shall get no love.
Lastly, If all this doesn't work, I think there are some type of pills you can buy from your local adult stores that will relax your muscles but, I don't have any experience with that.
This is not law, your experience might be completely different.