Never was much of loner, but I've always been pretty introverted and spend too much time on internet forums. I have to turn it on around people and it can get exhausting.

I moved to a new city after college and knew absolutely nobody there. Right before I left my brother told me a friend of his was there temporarily. I mean I hadn't meshed at all with this guy, he's a total shit-tester, but we didn't know anyone and started hanging out and now he is one of my long time blood-brothers. Through him I met a couple people and then some other people and eventually built some pretty big social circles, including my core. I point this out because the real key to entering any group is to just have someone vouch for you. You can be weird as fuck but if one person says he's okay, you are cool until proven otherwise.

Don't really have any specific advice, but I had the attitude of just do everything. If I heard something was going on, I'd always show up. I'd get drinks with the 30-something married guys from work, I'd hang out with weird stoner guys who took long walks, listen to the executive assistant yam on about her nasty divorce, someone at work set me up with an 18 yo high school girl (yeah I was that guy), went to a lot of shitty sausage fest parties, played pickup softball, went to random shows and talks that were in the alternative weekly, pretended to like college football because I wanted to hang with the guys watching it, went out to talk shit and drink too much espresso, hung out with fat girl orbiters, you name it. 90% of this activity didn't garner any long-term friendships, but the 10% which did mattered. And at least it gives you something to talk about, or an idea when a girl asks "hey what are you doing this weekend?"

(Re-reading that, I realize it was way more about male bonding and women were just part of the journey.)

Also "cocky/funny" party guy persona works just as well with men as it does with women. Especially in your 20s, maybe there's not many girls in the immediate area, but there always some beer and and going snowboarding and potential good times, and if you're having fun, maybe girls will come around.