For me, planning begins with a theme, or even just a "feel." For example, we had a Little Miss Sunshine movie night to ward off the icy coldness in the dead of winter.
A theme is a good place to start. Sometime themes evolve out of what it is that you want to do at said party (like the Little Miss Sunshine Party) or a couple years ago at Christmas when I threw a gingerbread house decorating party.
When planning a theme, consider your decorations, the activities, and the food.
My parties usually consist of people I see often, and because we do these semi-regularly, I skip the fancy invites and opt for something electronic (often facebook, email or texts, sometimes if I want to be "fancy" I'll send out an evite).
Parties can really be anything you want them to be! Although if it's a party by yourself, you might have taken that a bit too far!
Best. Picture. Ever.
Thanks for letting me share my bad jokes and party tips!
(I love the take on a more regularly recurring get-together... obviously for these types of occasions, things like invites can be a bit more casual, etc. Some fantastic ideas here for those non-kid parties! Can't wait to see the spa night and the bridal shower!)
Now you see why I'm letting everyone ELSE give you advice, instead of trying to do it myself.