Engagement Photos
Engagement photos are really just nice photos of the two of you together. They can be taken anytime prior to the wedding; they don't have to be taken right after you get engaged.
Often they're used for newspaper annoucements or displayed with a large mat around them for people to sign at the wedding (instead of a guestbook). They also make great gifts for parents & grandparents and to display around your home. The only reason I wanted them was because I didn't have many photos of the two of us together. (Any excuse for great photos of my sweetie!) Also, getting engagement photos done can be a great way to "test drive" your photographer. That way you can get a good idea of what they're actually like when shooting photos, and of course you'll get to see how the photos they took of you turn out.
If you decide you want engagement photos, the next step is figuring out whether you want them taken in a studio or on location. Personally I prefer having them done outdoors at a beautiful location, or else at a site that has personal meaning. But either way works. You also need to decide what sort of look you're going for. Do you want to dress up? Be formal? Be playful & casual? Both? (No reason you can't change clothes & go for a couple of different looks.)
Once you've figured out what kind of feel you want the photos to have, you'll need to decide what to wear for the engagement photos. Solid colors are best, much better than patterns. Patterns can be distracting and also are more likely to look dated as time goes by. Personally I'm not a big fan of wearing matching clothes in photos, I think it's better to wear coordinating clothes in a similar style instead. But lots of people like the idea of matching, that's really just a personal preference. I'd advise against really bright colors, against anything with logos or words, and against super trendy clothes. (Although it can be fun to wear some trendy clothes for some of the shots, and then change into different clothes for the rest.) Generally speaking people look better in clothes with sleeves, but that is just a rule of thumb.
Whatever you wear, the most important part is to relax and have fun. Having your own photo shoot can actually be a lot of fun. You can be silly, be serious, and be everything in between. And of course lots of kissing is a requirement of engagement photos, so enjoy.