Break ups are easy when we realize we are mismatched. Have some criterion about who you will let in your inner circle and make no bones about it. If you are incompatible then you are incompatible..Not worth your time and no need to waste theirs.
Become Healthy attract healthy. No reason to ever date a smoker or a drinker these days-just rule those two out to begin with and save yourself some heart ache. Set those boundaries early, no need not too. Look for signs of immaturity, require honesty. Trust is more important than Love any day. In fact for real love to be reason trust is a prerequisite.
Make sure you are on the same or close to the same page on religion, politics and social issues. Do you love team sports and he like hiking? Problems. All relationships have difficulties, but no need in taking on extras right off the bat.