well it depends on how good your soil is right now. I usually add some blackearth/compost to my beds yearly just to keep them healthy and full of nutrients. I swear by my garden claw...since I can't afford a tiller this thing works wonderfully well for working my soil over and getting things all mixed in nicely. Peat moss helps to retain moisture but it can alter the acidity/alkalinity of the soil so something like coir would probably be a better bet. (coir is made from coconut husks)

There are several things that can be done, depending on how much work you want to do.

The best thing for both immediate and long term benefits is the one that brings most work. Double digging. You first remove any existing plants from the bed and put them in a holding area. Then you dig down one to two feet, and amend the soil with lots of organic matter (compost), and good quality triple mix soil (or something similar), and put it all back in the bed. You now have a good quality soil very deep down and the roots can quickly spread out into it with the plants benefiting right away.

If you don't have the time or energy to do the double digging method, the easiest way to improve your beds is with compost, lots and lots of compost. You can pour it on to a depth of at least two inches and work it in as deep as you are able to. You can even leave it directly on top of the soil with no mixing in and the worms will eventually work it through (although if you have heavy clay the worms can take several years to do the job). Adding at least two inches of compost on a yearly basis will give you a much better result than almost any other amendment.

BP

I always refresh my beds with blackearth topsoil (mostly compost) and well rotten manure. Occasionally I would add peat but the top soil do have peat in it's mix.