My main tip is: avoind pairing up people that don't live in the same world. Like, its ok for 1 or 2 people to date online and have a distant relationship, but in real life most of those relationships fail when they turn into long-term distant relationships. If they are distant in the short term, they might work better, but also... not everyone moves town/country. So, I don't have a system of mine to "randomize" someone that would date and move worlds, I just roll a dice and see if it tells me yes or no.
Edit.: I forgot to say that sometimes i don't use the dice at all, if my sim likes to travel and meet new people, I just follow their personalities and let them move elsewhere.
Of course, you can play whoever you want, but its more realistic like that and it helps me to focus on creating relationships with people from the same town when the game does the opposite.
