I played a very active dating game, so there is no way i can remember everything, but i'll give it my best try:
Always be aware of what kind of friends the girl have. One of the girls i was dating had another guy who was close to her, who had been in and out of jail for severe cases of batterings (Literally jumping on peoples heads etc.). I had to disarm a lot of dangerous situations when i met him. Realize that some things just aren't worth it and move on.
Sometimes you will fuck up, and it will suck. Just move on. I once accidentally locked my date outside on a balcony at 11 pm in -25 degrees because i didn't realize the door auto locked. Shit happens.
The more people you know, and the more people who knows you, the more attractive you get.
And to follow up: Befriend fucking everyone, guys and girls. But also know when to say stop and when you've met some bad people.
As someone else said: Never turn down a threesome. Probably my biggest regret was when i was pushed up against the wall by two girls who wanted one, but ended up saying no because one of them had a boyfriend.
If a girl flakes on you twice, (Once if she's not that interesting), ditch her and just don't bother. Ignore her if she tries to ask forgiveness. You have better things to do than to deal with crap like that.
Crazy might feel so fucking good, but get out ASAP.
Keep a nice apartment. Keep it clean and stylish. It doesn't have to be complicated, or fancy (I furnish all my apartments with second hand things), just make it look good.
Stay away from drugs. Not only does it mess with your game, but also the girls you meet through drugs are boring as fuck. So many of my friends, who spent day in and day out smoking weed, complained about how i got so many girls and they didn't. One guy, who was constantly referred to as the "Hottest guy in school" kept having to ask me to help him out.
And for the most Seddit-oriented one: Flirt with everyone. Learn to make it part of your persona to be flirty. Whenever you talk to a girl, make sure she can't really be sure if you're flirting with her or not, because while you're talking to her as if you're flirting, you have absolutely no problem just turning around, completely forgetting about her, and talking with her guy friend, or "Flirting" with her friend right next to her. By doing this, you open the door to where you want, just a little bit, but you make the girls be the one who opens it. They think you're flirting with you, but they can't be sure, and they really want to know.
I have literally had girls lining up to make out with me at parties because i did this.