The main difference between me now and 20 year old me is that I'm no longer young enough to know everything. Or at least think that I do.
Let's face it, 20 years old is kind of a rough age. You're finally not a teenager but you're too young to legally drink and go to bars. It's like you're stuck in a limbo, just waiting to get older and be able to have new experiences. But it comes all too soon and before you know it, you're embarrassed to mutter "twenty-three" when asked your age.
The advice I would give myself at 18 years, 20 years and 23 years probably shares the same underlying message, work hard and enjoy yourself. Figure out what you want in life and then stop rushing the growing up part, it's where the mistakes are made and the fun is had.
I seem to drone on about how you should enjoy your youth, have all the fun you can and wait to settle down with one person... But the truth is, how are you supposed to enjoy your life when you have no idea where it's headed? At 20 years old, it's time to re-evaluate where you see yourself heading and what exactly you want to accomplish in the coming years. You've been in college for about two years now so it's time to make a decision, are you happy in your major? Or maybe you skipped college and headed into the workforce. Are you passionate about your field and want to spend the next 30-40 years exploring it? If not, what are you passionate about? Are you good at it and can you make a living from it? You don't have to know the answer to "where will you be in 5 years?" but at least figure out a general area.
Stop doubting yourself and surround yourself with people who won't either. I'd be nowhere without the support of my family and best friends (shout out to you guys, diva crew). We all need someone to call after a bad blackout, discuss a text message response with or cuddle on the couch in front of trashy television.
Purge yourself of toxic people and stop substituting real relationships for "party friends". This detox goes for men too, I know it's hard to let go of that one guy... The "bad boy"... The one you think is going to change for you... But cut the cord. You don't really want to be with someone who you have to change, right? Don't you want someone who's great just the way he is?
Chances are at 20 years old, you're still figuring out who you are. When I was 20 years old, I had just moved to Manhattan and was figuring out my life plan while trying to master the subway system. If I could tell myself ANYTHING, it would be "STOP SELLING YOURSELF SHORT! You can do whatever you put your mind to and though the future seems scary, you'll figure it out. Work hard, be true to who you are and people will appreciate that. Also, lose the nose ring."