Go to parties, but drink very little, avoid drugs, don't get caught up in sex. It's fun, but save it for later. Don't have a girlfriend at all, this is a time for lots and lots of friends.
I personally think the opposite. It's your 20s, enjoy it while it lasts.
Exactly, I used to think and practice like the OP did. You find that all your friends start transitioning into couple things and you are a workaholic who doesn't have any interests outside of work. Sure, that is fun and it will be exciting to spend all your time solving the nth problem in your work BUT life is not just that. Life is experiencing everything, yeah all that yada yada about doing it in moderation holds obviously but still. You can't just live your entire life, hope to be interesting to a wide range of people encounter adventures if you isolate yourself and not do any of this!
I'd rather live with the regret of 'Oh I wish I hadn't done this/that/the other' than being 50 and looking back on my life regretting I didn't enjoy myself more.
I personally think the opposite. It's your 20s, enjoy it while it lasts.