Hello, I was once a victim of the entity known as slenderman, I used to see him all the time, and I still do, but, he doesn't get close or even seem agressive, he is just passive,
Step 1: When he starts to freak you out, think that you are immortal, or he is just a guy in a morph suit who is standing on stilts, owns a pet squid named larry that he carries around, or, as I have done, imagine him as your Friend
Step 2: If the step above fails, I would suggest moving, or facing up against him, intimidation is key.
Step 3: If the two steps above fail, I would lock yourself away, repeating step 1, and keeping a toy with you,
If all the steps are not working, you have 1 choice, attempt to fight him, you will most likely die, but you should die trying,
Also, to keep your family safe, keep all portraits away from you, and the most important thing is to talk, he feeds on fear, by talking you calm down, making slender not really care about you that much,
It would be cool if anyone can post more tips, as for me, slender is still sorta following me, I know it won't work for long, he will get you, one way or another, or you can get him...