Some great advice has been given. Pay attention, listen, etc.
The ring is a symbol to both of you of continuation and renewal.
Buy one that she likes, and you can afford and do NOT go into debt!
Money is one of the prime causes of arguments for couples.
I have one other bit of advice. All people change as they progress through their lives. Some of those changes will not be to one or another of your likes. You need to accept that the person you love and marry is variable AND WILL CHANGE, as will you.
For It to last, you have to accept the changes and learn to "love the one you are with". (But not in the sense of the song). Don't dwell on the small stuff and let it get under your skin, and remember that it takes two to do anything together ( including arguments). Don't stress about who is RIGHT.
Marriage takes work to stay together.