Cling to your Rosary, the Sacraments, and the Mass.
Consider in earnest whether you have a vocation to the priesthood, religious, or married state.
Avoid alcohol (not being an heretical Puritan, but excess alcohol can ruin a person).
Avoid bars (whores, drunks, and the worldly hang out there).
Avoid people who are bad influences (whores, drunks, clean-cut staunch WASPs).
Avoid modern entertainment (music, movies, sitcoms, etc).
Find out what you're good at/enjoy for earning a livelihood (keep reality and fantasy in check).
Don't think that your twenties are a time to be a man-child--in previous generations men (respectable men rather than thug boys of today) were fathers before 20 or very early 20s. Fɾҽҽmαsσɳɾყ/Jєωry dictates a college degree (4 years filled with promiscuity & debauchery) for stocking shelves. That's not to say nobody should get a college education. If you have an aptitude for medicine, law, accounting, engineering, etc. fields that require college, then stay focused on why you're there and don't fall into the traps of substances, whores, etc.
If you are to marry, figure out how you're going to meet a good Catholic. I wouldn't rule out the possibility of converting an appropriate young lady. But it's probably not advisable to set out with that as your primary planned course to marriage.