A tea party can make a very fitting theme for a bridal or baby shower, or even for a birthday party. They also can be relatively easy to throw, as the focus is on finger foods. If you want it to be a more genuine tea party, probably one of the most difficult parts is in finding enough tea cups for each guest (and I don't mean mugs, I mean tea cups). Luckily when I threw one for my friend a few years ago her and her mother had a large collection that we could use.
Don't worry about all the tea cups matching, in fact that's part of the fun. That is how it is traditionally done in English style tea houses anyway.
So, to begin with invitations, there are lots of choices out there now for tea themed invites. Just do a Google search and you will find plenty. Dori Ann's offers a large variety in particular.
If you want to opt for something more personal; however, it is pretty easy to make your own. I simply cut out a tea bag shape and printed on it "You are invited to a bridal shower", and attached it complete with a string and tag (even with a staple in it to make it more genuine). This is a good option if you are particular about the colors.
It is important to set the mood for the tea party by playing a little soft background music. Of course if you are opting for an English style tea party, go with classical. If it is more Asian, find some traditional Asian music.
As mentioned before, tea parties are an easy way to get away with just serving finger foods such as small tea sandwiches and scones. Don't forget that if you are hosting this party over a meal time, have PLENTY of finger foods. Enough that guests could eat at least a light meal's worth.
As for serving the actual tea, you can simply set a tea pot on each table either with tea already in it brewing, or opt to give guests more options, and set a tea pot of hot water on each table and walk around with a tray of individually wrapped tea bags in a variety of styles (make sure to offer a decaffeinated option).
It is also a good idea to offer a couple other types of beverage, because frankly, not everyone loves tea. Punch is a good traditional English party drink.
Dessert could be as simple as small tea cookies, or a little more elaborate like petit fours, chocolate dipped strawberries, or a more standard cake topped with a cute little tea cup.
Decorating can be simple, too. A small pot of tea roses for centerpieces would do just fine. If you opt for something more elaborate, topiaries are very English. I found wire "tea pots" at plumparty.com and made my own with that as the base. I recommend Plum Party for a tea party because they have some interesting supplies. Check under "themes" and then under "bridesmaid, brunch, tea".
There are lots of ideas for tea themed party favors, too. You can find some at the rosemarycompany.com, beau-coup.com, or theknot.com in their wedding shop section.
As always, refer to the "General Party Planning Tips" post for some basic guidelines. Enjoy, and happy planning!