TeamSugar member aistea311 recently posted one of my favorite tips. I live by this one every day and definitely think it's worth mentioning.
While it is a super simple tip, it's definitely one worth keeping in your repertoire. If you don't have fresh lemons or limes on hand, you should consider keeping a bottle of 100% lime or lemon juice on hand. I personally have both, and find that it's a nice treat to be able to spruce up my water. Plus, guests are usually wowed when they ask for water and you say, "plain, with lemon, or with lime?"