Slenderman Summoning

Good afternoon ladies and gentlemen and anything in between :D

I'm trying to figure out how to summon Slenderman but I'm kinda stuck :p ive got no clue how to do this  ive only summoned ben before and i dont even know if that worked lolz. So I would really appreciate if some people could give me some methods!!! 

Things I wont do:

✃ Anything at night

✃ Blood (if I need to i will)

✃ Forest (i might but id preferably not do it)

Anyways!! Thank you! Have a nice night!

Love Colton (//_¬") ♡