Getting together with friends shouldn't be a fussy affair. If all you have the time and energy to do is send out an email, then offer to host a potluck dinner at your place and get the gang together for a night. Being the potluck host doesn't let you off the hook completely, but it's a heck of a lot easier than cooking for a crowd.
The first step to a potluck is sending out the (informal) invitations. And the modern way to do that is online. There's likely already a precedent in your friend group for announcing events, so go with the flow—whether it's a text, email or Facebook event invite.
Name the time and place, then ask people to let you know as soon as they know what dish they'd like to bring. There are websites that can make quick work of this—like Sign Up Genius or Thing to Bring—but the very best method, I think, is just a quick roll call via text, email or comment.
Modern Potluck Tip: You can plan the menu, but not too much. If you're after a truly casual potluck, your only goal is to make sure there's a variety of dishes and that no course—from appetizer to dessert—is left behind.
Accommodate (and Share) Diets
These days, it's likely that more than a few of your guests are coming to the table with dietary restrictions or food allergies. If you don't already know your friends' needs, ask in your invitation that they follow up with restrictions—and to let you know how severe they might be.
Inform the whole guest list if anybody has the kind of allergy where a whif of peanut dust means a trip to the emergency room, but also be cognizant of more mild needs. That guest will likely bring a big dish that they can enjoy, but the very best host will make sure there's something else at the potluck for them, too, even if it means leaving the shrimp out of the fried rice.
Get a Handle on Oven Time
The number one thing most likely to guide a potluck off the rails is when the oven at the host's apartment becomes overbooked. See, guests sometimes bring dishes that need to be re-heated or finished off baking before they're served, and that can mean trouble when the oven is the size of a shoebox.
When you find out what dishes guests are going to bring, you can follow up with them individually to suss out if they'll need the oven to finish their dish. If they can estimate a cook time and temperature for you, you can use your notes like a playbook on the night of the potluck to make sure everyone's dish is served piping hot.
At the Potluck:
Provide Plenty of Drinks
As the host, this is your number one responsibility. With a potluck, the menu ends up all over the place, so you really just need to plan to stock a variety of drinks for every taste—there's no wine pairing when buffalo sliders end up next to sushi. Pick one red and one white wine, plus a variety of beers—I swear by the "3M" rule: One mass-market, one microbrew and one Mexican beer.
Have Servingware on Hand
Guests will arrive with empty bellies and soon-to-be-warm dishes, but the one thing they won't carry with them to your potluck is serving pieces. Make sure you have at least one big spoon on hand for every dish at the party, plus maybe a few extra spatulas, too. Your usual kitchen gear is just fine as long as it's clean, or you can pick up some plastic wares from your local party supply store. The potluck is a casual party, remember?