soaking the beaver tails is almost always a must, but depending on what leather you are using, it may not be necessary.
The glue is great help in that it will hold your piece in place while you form, and cut it. Draw an outline on where you would like to trim using a pen or wax pencil. Use a razor blade to trim, but be careful to pull up on the leather as you are triming so as not to cut into the finish of the bow.
Dont spread glue on the back side of the grip (portion where your fingers overlap). This will allow you to size, trim and mark and then peel back to punch holes without removing from bow. Glue there before sewing.
it is ok to leave a small gap where the edges meet with softer leathers, but you will never pull that gap shut when using Beaver.
If you are using regular leather, it is usually cheap enought to redo if you don't like how it turned out. Not so with Beaver.
I have done several hundred beaver tails in this way and found it to work well for me.
good luck, bigjim