How do you get your sims out of the house?

I have City Living, so I send them to the festivals that pop up. If you haggle with the vendors you can get food for cheap sometimes, and the Spice Festival has free food, so it doesn't cost anything at all. There's music and weirdly-dressed Sims, and I almost always go, despite my usual avoidance of loading screens.

I usually invite as many Sims as it'll let me, to keep up relationships.

I send my kids to the parks. Sometimes the teens too, though of late I've used my teens to explore the non-lot areas looking for collectables. YA and Adults go to the clubs and bars (I don't have dine out or city living yet) Elders... Elders do any of the above.

I mostly have my sims go to a bar. When I get tired of that, I have them cook a group meal, make sure it's not horrible, and go visit a random household.

Where (and how often) my sims go out depends on their personality and lifestyle. My main sim is a busy stay-at-home parent/freelance writer who lives with his partner and their clingy toddler, so admittedly finding time to go out doesn't happen too often! They also live in Brindleton Bay and since it's spring at the moment they end up having a lot of rainy days in. He has a close friend/neighbour who is also a stay-at-home parent and they sometimes arrange toddler play dates at the park or go to the spa together for some quality 'wellness' time. I find watching my sim relax at the spa really relaxes me as well. My sim is also into fitness and likes jogging around the neighbourhood with his earbuds in. He also goes on family days out at the toddler park when his partner is off work, and I like to make sure they still spend time together as a couple and go on dates at restaurant, lounge, bar, museum and romantic garden/park venues. They sometimes go on family holidays to Granite Falls and at some point I plan for them to visit Selvadorada. Now I have Island Living I will have to take them on family beach trips too and maybe holidays in Sulani using a generic 'hotel' venue. My sim is also on his way to becoming the leader of the Avant Gardes book club and goes to regular gatherings at their café hangout. I plan for him to buy a book shop once his toddler ages up and go there to write and sell his books.

Restaurants are bugged for me atm. Sims stealing one another's food and what-not. And you're right OP, it is expensive. That's why I like parks and nightclubs. I also built a community lot that has a lot of the skill building items that I can't put on every residential lot: like the cupcake machine and observatory. I like spas as well because like @annaliese39 said I find it relaxing to watch my sims relax. Now that pools are a little more worthwhile I've found a public pool on the gallery and my sims actually spend time at the pool now! With Island Living I also enjoy just going to the beach.

I quite like visiting libraries and retail stores. Also the gym and pool. And the beach too, now that we have them.

Taking advantage of any community lot in any of the 'wolds'. Prowling the non-lot but accessable areas is often good for meeting folks and stuff to collect. Sometimes free food as well. Going for walks anywhere you can get your sim to go works as well

Normally, I find my Sim a mate and then they won't socialize with people outside their household anymore. I would rather do other things with my Sims than have them socialize. But sometimes, I'm in the mood to have them throw a little party for a handful of people - they can be family or just a few Sims I like.

For single Sims, I might use customized bars. Nightclubs usually have old people as DJ's which I find annoying. I actually feel most community lots don't function properly anymore. NPC's are just a nuissance to me. They don't behave, and so I don't want my Sims to be near them. They steal food and drink and invite themselves to my Sims' conversations and into their homes.

I always find the gym in Willow Creek a good place to socialise. I have my sim work out first then socialise. There is always loads of sims there. Also any of the nightclubs in Windenburg are great. Always plenty of sims to socialise with. Libraries are great too. Then once I have made lots of friends and aquantainces I throw parties at home.

If you want to socialize go to the park... No one will leave you alone. Not even it you play an evil vampire with the worst reputation and the uncontrollable hissing.