This step is probably the hardest for most people, considering almost everyone has more than one Waifu. My personal choice is gonna be Senju Muramasa from Eromanga Sensei for obvious reasons.

This is a easier step and is quite simple. You're going to want to think about your Waifu as much as possible. From the second you wake up to the second you lay down and go to sleep. You going to want to get to the point where you're thinking of her even when you don't mean or want to.
Spamming the show or game where you Waifu came from is sure to help as well.

Now all that's left is to lay your head down and dream away. Depending on how much effort you put into step two, this could take as little to 1-3 or 10-20 tries at most before your Waifu appears in your dreams. There's a slight chance that your Waifu doesn't appear but instead another anime character does, at this point you're going to want to try to date them anyway because let's be honest this is as close as you're going to get to ever dating a anime girl. Thanks everyone and have fun dreaming! Zzz..