That's a big question and the best answer I can give you is to start closing the sale from the start of the selling process.
Once you have qualified the prospect as a person that could have a need for your products, now or in the future, build closing into your communication with them.
There are sales closing techniques that you can use to gain agreement right from the very start of the sales process.
These selling techniques will all stack together so that when you get to the stage where you ask for the order you will close more sales.