Let’s start with some awesome theme ideas:
I personally think, if you’re planning on throwing a surprise party for one of your girlfriends, a donut or ‘not a morning person’ theme would be ideal for any season. A fruit themed birthday would be super cute in the summer. If your friend’s a leapling, make it a frog and lily pad theme. But like, don’t overwhelm them with frogs.
After you’re done choosing your theme, send invitations to go with the theme. (Well, unless it’s a surprise party:)
Games: No one can have a party without them.
Possibly some pranks…
Cake! What’s the point of a birthday of you can’t eat cake?
Finally, all the guests are fatigued from a very fun day. I dunno about you, but after a party, favors are nice.