Dear Rajesh Adams,
You do not have much time left to prepare. Here is the protocol:
Maybe you stay in the bedroom and you change into your night dress. Take the opportunity to use the toilet and to freshen up. If you get nervous, and nervous sweat isn't good, so wash your armpits and your crotch. Put a tiny bit of perfume behind your ears, in your navel, and behind your knees.
If she is coming in formal, let her changer her dress to nighties. Go to her, hug and kiss her. Rub your hands up and down her back. If she is willing to prolong this, great! Rub your body against her as you kiss. Pretty soon, you should feel your erection against her belly. You step back at this point and undo and remove her dress and yours, and then return for more hugs and kisses. Now you signal or turn toward the bed. One of you should turn down the bedclothes and get in, then the other gets in and lies so you are side by side, facing each other.
Tip: You want her "good" hand to be on top when you are lying on your sides facing each other.
Tip: if it's a small bed, try to arrange her position so she is mostly centered on it and you are lying on your side in the narrow space to her right. If she ends up on top, she'll have to rearrange this, but if you end up on top, she want to be in the middle for balance.
Warming each other up in bed
As she kisses facing each other, you use your free hand to rub her back, butt, breasts, and thighs, and then start to explore her belly and groin area. That's her signal to roll so she is on her back, and to open her legs a bit wider so your hand has access to her vulva. You start to rub and stroke. If you need guidance, put her hand on yours and help you adjust the position and pressure.
The main event
You use your hand to guide your penis into her vagina. If you are not quite sure where it is, this may involve a lot of fumbling and shifts in position. She can help by pulling her knees up and out to the sides to make more room. Once you get the tip in the entrance, you SHOULD insert it the rest of the way very gradually, but you will probably just thrust hard instead, in which case she 'll probably feel a brief, sharp pain.
The position you end up may be missionary. i.e You are on top. or if you prefer more of a kneeling position and can get your knees that far apart:
In this position, you can thrusts your penis in and out by flexing your hips and lower back, so it's a good position for sustained sex with a lot of intimacy. She can control the angle of the penis in her vagina, which affects how much sensation it gives to her, by moving her knees up or down, more toward her shoulders or more toward the foot of the bed.
Some women like to grab their thighs and pull their knees all the way up against their chests or biceps, raising their hips up off the mattress. This is a good position for getting pregnant if she stay that way after you ejaculate, because it reduces the sperm leaking out. It is also a good position for a man with a smaller penis, because it allows deeper penetration.
The opposite position is where she straighten her legs more, slide her feet further down, and arch her back. This tilts the pelvis the other way and creates more friction for her vulva, but it reduces the penetration depth, so it is better for a man with a longer penis.
When you come
But first times are usually very quick, so she probably won't get a chance to experiment with positions for her legs until later. For the same reason, don't expect much in the way of pleasure from the actual vaginal sex the first time. If you are virgin, you are so overwhelmed by the sensations that you may ejaculate very rapidly. In fact, it's not uncommon for a bridegroom to actually ejaculate as soon as his penis touches vulva, before you get it in at all!
If that happens, don't worry, remind yourselves that there's no hurry, and then cuddle with her and talk about what an amazing, crazy day it has been, or how strange all this is, or whatever she want, until you get your second erection and she can restart the program where she left off.
If you are uncertain or upset, take your face in her hands, kiss her and say, "I can't believe how lucky I am to have you for my wife!" That will usually resolve all of a woman's feelings.
You may want to have sex several more times that night, or she may be too sore or she both may be too tired, in which case, you should wait for another day to do it again.
What if it's not like this?
There are so many ways things could be different from what I just described that I couldn't possibly list them all. If your fiancé has something radically different in mind, ask her to explain what she wants and discuss it with her if you don't understand or don't want to do it.
Other than that, do what all newlyweds do: fumble around and improvise! And if things go wrong, be patient, be ready to laugh with her and reassure her that there's plenty of time - you've got a lifetime to get it all figured out!
Okay, I hope it helps. Whether it does or not, congratulations on your upcoming wedding! Have a wonderful first time and a great marriage!