Hello. I agree with Thomas and John. "Making friends is always hard FOR me" is correct.
Also, this is such a complex topic, because one can use "for me/to me" in multiple ways. Sometimes both can even be used interchangeably. However, I will try to give you a simple answer with A LOT OF EXAMPLES.
"FOR ME"-->it's your EXPERIENCE/it's something that you do or have done before
----------Ex: Making friends is always hard for me. *It's hard, because every time when we talk we have nothing in common.
-----------------It's always hard for me to make friends.
----------Ex: Talking to strangers is easy for me. *I've talked to strangers before and I love making new friends. Talking to strangers is something that I like to do at parties.
-----------------It's easy for me to talk to strangers.
----------Ex: Driving a truck is hard for me. *Because when I drive, the road looks narrow and I keep going towards the opposite lane.
-----------------It's hard for me to drive a truck.
"TO ME"-->it's your OPINION/it's something that you didn't or haven't done yet.
----------Ex: Making friends seems hard to me. *I haven't tried it before but I think it's hard, because you have to initiate the conversation. You also don't know if the person will be friendly or not.
-----------------To me, making friends seems hard.
----------Ex: Talking to strangers seems easy to me. *I haven't talked to strangers before, but my friend always does it and he makes it look easy.
-----------------To me, talking to strangers seems easy.
----------Ex: Driving a truck looks hard to me. *I haven't tried it before but I think it's hard, because when you speed you have to be careful and if you're not, you could crash.
-----------------To me, driving (a car/truck/van/etc.) looks hard.
Hope this helps a little. :)