There is the usual way to gather – sew a row, pull a thread – but there are easier ways.
The first way is to give yourself a very definate thread that is very easy to pull. To do this you just use the zigzag stitch and a piece of something like crochet cotton. You can use a bright colour to make it easier to see as you will probably get rid of it when you sew the gathered part to the band or whatever it is you are going to attach it to. Here is a video to demonstrate. Click here (will open in a new window)
Another, even easier way is to use a piece of elastic. For example, if you are attaching a skirt to a band and you want the top of the skirt gathered evenly, cut a piece of elastic UNSTRETCHED the length of the band. Then spread the elastic evenly along the bit to be gathered, using pins to hold at 4 places and stretch the elastic as you sew to take up the material. Here is another demonstration Click here (will open in a new window)
The finished dress (nothing special, just made to test my pattern)