I think the trick to a lovely evening is to think about what you can do in advance - whether that's food prep, table setting, drinks laid out etc. I try as much as possible to avoid notable cooking after people arrive, and if I must, it's quick things that are all prepped - eg in summer with a BBQ I'll quite often do things like garlic prawns for people to nibble on while sitting around but I don't cook them until everyone arrives but I have the oil in the pan ready to go, a bowl of garlic, lemon zest and chilli and a separate bowl of chopped parsley - so I can pull it together in less than 5 minutes with no last minute chopping or looking for things.
I think it's essential to offer drinks pretty much as soon as people walk through the door. You can have a drinks section set up or just have open bottles ready to roll and hand over to people (sometimes I make up a batch of a cocktail and offer that "Margarita or a glass of champagne?"). n that note, I think bubbles or a cocktail create an instant "party" vibe but aren't essential. Similarly, nibble sof some sort help to break the ice, give people something to do with their hands and/or a conversational starting point - doesn't have to be complicated, smoked salmon on blinis or even just crisps and dips.
Cook things that don't have to be portioned out perfectly and/pr that you can pile on the table to help themselves. Don't be like a flatmate I had years ago who managed to kill eevry dinner party by obsessively serving up a single lamb chop, 3 potatoes and 5 pieces of aspargus - it took forever and inevitably felt stingy.
My sister, who has more space than I do, also is fantastic about making things look a bit pretty - so she can set a table and leave it set up with lovely place settings or centre pieces and again, I think it creates an instant atmosphere when people come through the door. The closest i can come to that is to put my lovely lamps outside the front door and some flowers on the windowsill! 