Well, as far as tips go, I'd recommend analyzing your proposed bathroom vanity space before you decide on one for your home. You don't want your bathroom to look too cluttered with an over-large vanity, and on the other hand, you don't want a tiny vanity either... it just looks awkward surrounded by all that open space! Take all appropriate measurements, and if you can, go to a vanity showroom or a home design store and see how certain vanities look in confined spaces. This should help you gauge an adequate vanity size for your own bathroom.
Additionally - and this is just personal preference - I'd recommend looking for double bathroom vanities (here are two of my favorite vanity retail companies for design inspiration, etc. : http://www.bathgems.com/ and http://www.tradewindsimports.com/ ). Double vanities are large, but they offer two sinks and plenty of countertop space -and believe me, when you live with a partner, all that space is necessary! It's such a relief to know I don't have to "wait" to use the sink. If you have the space, definitely try it out!
As far as design concerns go, that is completely personal. But look through those sites I posted above and see if you find one that catches your eye!
And careful with whom you buy from. Madison is partially right: MANY modern bathroom vanities are eco-friendly and feature sustainable, durable construction. But many cheap-o companies prefer to skimp on quality and sell "modern vanities" that fall apart in little time. So before you buy, do your homework and find out if the company you are buying from can actually walk the walk, not just talk the talk!
Hope this helps! :)