A Groom’s Guide to choosing an Engagement Ring

Since traditionally the responsibility for buying (and choosing) the engagement ring rests with the groom, you need to make sure that you are clued up on all manner of things: stones and their clarity and colour; different metals and their durability, settings and styles, fashions and trends.

However, the greatest responsibility as the groom is that you need to make sure that you are certain what your bride will want. Besides her ring size, you need to know her taste in these matters: whether she likes the traditional yellow gold, or would prefer platinum or white gold. If her taste in other wedding jewellery is simple, she is more likely to prefer a solitaire; whereas if she enjoys startling, eye-catching items, she may want a more modern, unusual ring sporting perhaps a cluster setting or a band of stones. So, if you want to do the romantic thing of getting down on one knee and holding out the little velvet box, you need to do your homework.
It's still not easy to make sure you pick the right ring – and after all, she is going to wear it for a very long time. So - if you are worried about not getting the choice right, you could arrange with your friendly wedding jeweller to have a pre-selected range of rings (priced right for your wallet) just waiting for the two of you to walk in and make a selection.  It sends the right message to your bride: that you really want to consider her in this most important decision.
On the subject of cost, what should you be spending? The concept of two months’ salary is one which dates back to 1947 and diamond giants De Beers who were trying to promote sales after the slump of the war.  Together with the slogan “A diamond is forever” they made it known that they wanted to make diamonds affordable for everyone, rather than in the hands of the rich only, as had previously been the case.  So, despite growing inflation, the idea of spending two months’ salary has remained a fairly constant one. 
Another selling point for the expense is that diamonds are an investment. I’m not sure that your bride will see it that way, when you ask her to sell the investment some years hence, to buy a business.  Just see the diamond as an investment in your marriage.