Simple does not mean boring, in fact far from it. You can still WOW your guests by just following a few basic rules.
As long as you have enough food and drink along with a great atmosphere, your party will be a success.
This doesn't need to be complicated, choose simplicity. Try not to over complicate the setting either.
Suggestion - inspired garden BBQ
Avoid - strategic fancy dress
Decide if you are doing a dinner, buffet or just hors d'oeuvres as this will really impact on how much time you actually spend with your guests.
Also try choose foods that can be prepped earlier in the day to help you out. Dinners tend to be for a much smaller group than 30, so a buffet style might be your best option. Plus you can do indoors or out. However if cooking is not your thing, then a caterer or takeaway is the way forward for sure.
Suggestion - if budget allows, get someone else to worry about the food
Avoid - hot foods that need cooking from scratch and need to be served up straight away
If you have a smaller space, then a cocktail party could be the way to go, as most people will be standing, plus with a cocktail party you could just serve small bites, however a buffet can be flexible with both standing and sitting.
Suggestion - if you can, have the buffet in an adjoining room, where guests can enter and exit easily without bumping plates
Avoid - a large dinner party in a small space, as you will need to find seating for everyone
DRINKS DRINKS DRINKS
Make sure you offer a well-stocked bar and include non-alcoholic beverages. You could even set up a self serve bar, or if you really want to schmooze your friends, hire a bartender.
Have the freezer full of ice, and a hidden stash of extra drinks, in case it does run low.
Suggestion - solicit a friend's help to make cocktails while you greet your guests at the door
Avoid - trying to frustrate the neighbours as the drinks start to flow