There are so many different ways dancers prepare their pointe shoes.
Ultimately, you will have to find the best way that works for you. Here are, however, a few tips that work very well for most. These tips are for conventionally made pointe shoes.
First of all, try the shoes on and figure out where you would like them to be softer on the box so that you can use your demi pointe. Hold your shoes in your hands and put your palms over the wings of the shoes (where your little toe and big toe’s joints would touch) and very gently push down on the box. You will feel the box move but make sure you do not push too hard. The warmth of your hands will soften the glue and make it easier to soften and break in. (Do you know what is inside your pointe shoes? See another entry https://kodamaballet.wordpress.com/2012/09/22/what-is-at-the-end-of-pointe-shoes/ ) As the glue warms, you will start feeling the box of your shoes moving slightly under pressure.
Next, hold just under the middle of the rim (if your shoes have drawstrings, just under where they come out) with your thumb inside and place the side of your forefinger across the top on the outside, as if to make a T shape. Your thumb should be aligned with the shoe’s length. Gently, using your forefinger as an axis, lift the centre of the shoe, where you would like to bend when on demi pointe. Do this several times but just a little bit at a time until it is a little softer.
Put one hand inside a shoe, palm down, and put the heel of the other hand against the sole of the shoe where the ball of your feet would be (about a third of the way in from the toe). Rest the top of the box of the shoe down on the floor and push it towards the floor with the heel of your hand while the hand inside the shoe is pushing away from the floor. Do this gently and gradually until you know how the shoes react. When you get used to it, you should be able to do this with just one or two pushes.
Hold the shoes about a third in from the heel (around where the round bit of your heel ends) with your fingers and gently bend both ways. If you use shoes without stitches, you could dislodge the glue and get the inner sole (only about a third of it) away from the base and in this case you will often see the shank. Even with stitched shoes, bending the sole in this way will enable the back of the shoes to move along with the feet better.
Next, hold the middle of the shoe, where your arches are highest, and gently bend it both ways.
All the while you are breaking your pointe shoes in, do it gradually and gently. Try your shoes on often to see how they feel. You do not want to bend them in the wrong places or too much. You will get used to it very soon and you will be able to go through this process very quickly and efficiently, but until then, play it safe.
There are several other things you could do. You can score the sole lightly with a knife to stop the shoes slipping too much or you can darn the tip of your shoes. I never felt the need for either of those things, but often the satin on the tip of the shoes will start lifting when you have used your shoes for a bit, and when this happens I would cut off the satin from the tip and quickly darn the edges to prevent the remainder from lifting.
These are just a few guidelines to start with and you should find your own way to make your pointe shoes as comfortable as possible.
If you are a complete beginner for pointe work, you should not try to break your shoes in before you have showed them to your teacher and got their opinion as to whether it is all right to break them in a little. Often it is best to learn to break them just through normal use at the beginning, even though it takes quite a bit of time.