Go to Tiffany's if you have one near you. They offer a free video, "How to Buy a Diamond." (Of course, they hope you will come back and buy the diamond from them. In my husband's and my case, it worked.
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You will want to think about your wedding ring at the same time. Do you want a wrap or a separate ring? What color wedding ring do you want? (You should get the same color engagement and wedding ring if possible - but you don't have to pick out both rings definitively now.) Are there any religious restrictions on your wedding band? (Some religions require a plain, unadorned band - in which case you may want more jewels on your engagement ring.)
KappaStarGirl makes a good point about your job - though I will add that in certain jobs, it is unsafe to wear a ring at all. In that case, you can do whatever you want with your ring, knowing that you will only wear it on social occasions... or you may wish to look for some other jewelry item (pendant, watch, etc) as a token of your engagement.
If it helps... my husband looks good in gold, I look good in silver tones. Picking out our rings was hell!
My engagement ring is a traditional Tiffany-cut diamond in a platinum setting. His is several small diamonds, channel set in gold. Our wedding rings are matching yellow gold bands with a white gold design.
Early congrats and happy shopping!