I haven't used this as often as I should yet, but here's one type of medidation I found particulary relaxing and mood enhancing.
I actualy forgot the proper name for it, its a buddhist practice of progressively trying to show love for everything, that supposedly helps to tone down anxiety.
First, make sure you're relaxed, in a space you can feel safe and calm in, like your bedroom. Position yourself in some way you find confortable (you can also lay down if you want), and then try to just be quiet and push away all thoughts from you mind for a few minutes. Do the basic meditation techniques, like controlling your breath and getting into a certain position. Remember that the position ultimately doesn't matter, as long as its one in which you can remain still for a long time.
Now, attempt to do these things, in this order.
1-Think about a thing or a person you really like. Spend some time thinking about why and what you like about this thing/person, and just generally enjoying the thought of being with that thing/person and wishing good things for that person/things. If its a person, generally try to think about making that person happy and enjoying their happyness. Wish these things to happen, and spend as much time as you want doing this.
2-Think about yourself, who you are, what you can do, what you like and dislike about you. Think about your successes and your mistakes through the day. Try to forgive yourself for you mistakes, and commemorate your success. Try to like yourself, find your qualities and relish in them, while also fully knowing your flaws and thinking of way to improve them. Picture your ideal self, spend some time enjoying the feeling, and wish it to be real.
3-Now, try to think about something or someone that you're indiferent about. If its a person, think about why you're indifferent of that person, think about how you could improve your feelings for said person, try to put yourself in their shoes and consider their condition. Then, start trying to like that person, in your mind. Imagine yourself making that person happy, and partaking in their happiness. Do this at least for a little bit, until you're actualy enjoying the thought of seeing that person happy, and then wish it to be real.
4-Now, this is where things get difficult. Try to think of someone you actualy don't like, IE someone that causes you problems or just someone you just can't put up with, an enemy, anything like that. Now, try to put yourself in their shoes and think about why you don't like that person. Now, start thinking about forgiving them, making ammends, etcs. Start thinking of them being happy, and you enjoying their happiness. This is the hardest part thus far, and not being able to do this at first is completely normal.
Keep doing this, but try to do this in relation to everything in your life, be it people, things, ideas, etc. Doing this every night before sleeping is actualy pretty great and can do wonders for eliminating anxiety. There is some real study on this meditation technique that shows that this can have some pretty positive effects in the long run.
I actualy read an article about this last month. I'll try to find it again.