Looks have nothing to do with personality. That's a separate criterion.
There is no definition for a "good" personality. But it can be said that people flock to persons who make them feel good about themselves and good about their lives. That doesn't mean the person has to be a psychologist and therapist. For example, if an acquaintance invites you to go skiing, and you've never been before, but he encourages you, and doesn't ridicule you, and doesn't abandon you so he can go have a good time on more advanced slopes, then you're going to have a good time, and you're going to feel pretty good about things - because of that person. So he might be ugly, and he might not be all that funny or clever - but you're going to like hanging with him and if asked, you'll say "he has a great personality".
You can't just say it's because he cares for you, or he makes you laugh, or he puts others first, or he has a lot of integrity - or any other single act. It's just that you feel good being around him, due to what he chooses to say and do, and the activities that he shares with you. Those are the things that - taken all together - we mean when we shrug and say "he's got a great personality."
If you are seeking to develop this mysterious trait, then just use your imagination and consider all of the people around you as people in need. They each have their own worries and insecurities that they deal with every day like a weight they've gotta lug around. See if you can come up with something to give them a break so they don't have to think about that stuff, at least for awhile. Show them some fun, and enjoy it because chasing their problems away helps chase YOUR problems away. That's all it takes. Do that habitually, every day - then YOU'LL have a good personality.