Shopping for an engagement ring can be a puzzle, especially if its your first experience (and hopefully the last) Here are some things to consider.
Some say, the engagement ring is one of the biggest spending you will ever make into your future. Don't get too much into the investment concept of it. Appreciation of jewellery works little different than real estate and it's only a sales tactic. There was a tradition developed that states the ring should be 2 months worth of your salary. This shouldn't be taken as a rule of thumb though. Its whatever your comfortable on spending. If your making average income you probably want to spend little more than $50. However, any woman who enforces or takes the 2 month rule seriously should be thought twice about getting engaged or married too.
Oval shaped ring will soothe better for short fingers. Choosing a big ring for small hands will make her hands look even smaller. Woman with larger or longer hands are more bound to larger, flashy diamonds. Choosing small rings for larger hands will draw out attention to the hands. Now, technically larger rings cost more, so consider yourself lucky if your girlfriend has small hands. I bet you didn't think about that when you begun dating her.
Heavier and larger rings many not be a good choice for anyone who works with their hands. Flashy and big rings are also inappropriate for some professions, such as social workers or counsellors. Spiky, sharp could be less practical, as they are more likely to catch on clothing or cause an accidental skin scratch on someone or even yourself.
Taking above into consideration, be realistic, pick your budget, pick the shape (Pear, oval, emerald, princess, marquis, trilliant and heart), pick the cut, carat weight, colour (colourless, brownish, yellowish, greyish) clarity and mostly important make sure you are ready to get married!