Now that you have your paper and paints and have practised a bit, you will probably want to paint a picture and in all probability, you will want to make a drawing on your paper before you start - unless you are a very free-spirited painter! How do you erase any mistakes you make? - you don't!
One big problem with watercolour paper is that the surface is delicate. This means that if you start erasing your pencil marks, you will damage your paper and when you paint over the area, it will leave an unsightly mark where the paint reveals the scrubbed surface. You might try the kneadable putty eraser rather than the normal type of rubber (whoops, sorry I think that's rather rude for my US friends!) - I mean of course eraser. I can't get on with this type of eraser myself as I find it leaves a slightly greasy surface to the paper so just use a small, soft rubber eraser. Why not get a piece of pre-soaked paper (make sure to use a piece pre-soaked as it's surface is more delicate then and will give you an accurate result) and try varying degress of pencil pressure and then erase them (I keep having to change my wording to 'erase' with this piece!!) When you then paint over these areas you will see how much you can get away with. You will be all right with very light pencilling. However, after much trial and error, I now draw onto tracing paper instead and then just transfer this to the paper as I had too many sheets of paper wasted when I drew straight on to the paper. Now I can erase my pencil marks to my heart's content!
Watercolour painting entails a lot of control - even in apparently free-flowing pieces, so all the practising you do now will really pay dividends. You will have a lot more confidence when you feel even just a little bit in control of those beautiful watery colours. If you have practised you will already have made some discoveries - that watercolour dries lighter than when you apply it, for instance, unlike acrylics which dry darker. You will probably have found that when you start to mix more than two or three colours together you always end up with mud! One of the challenges of watercolour is to retain its vibrancy - particularly difficult in paintings like mine which are made up of many layers, as of course the natural tendency for the paint when overlaid with another layer of paint, is for the two lots to dissolve together and it is very easy when layering watercolour to end up with an opaque, muddy mess, but don't worry, with a little help, you will soon be producing paintings you are proud of.
The pictures I am including today were originally intended to be for my website but I forgot to keep taking photos as I went along!! The 4 photos show a) the pencil drawing (I hope you will able to make this out), b) a few washes in c) more work on the eyes d) the finished article. For those who wondered, he is a lurcher - a really lovely friendly boy I had the pleasure to meet when his owners came to pick up the painting.