i just started painting a year ago. before then i had never grabbed a brush. just decided one day to try it and i have enjoyed it ever since. but i have a problem. i want to learn to stretch my own canvas because i want to make a really large large painting and i haven't found one that large that anyone sells. where do i begin? and so far i have just been putting paint to canvas, are there any preping techniques that may enhance a painting? i've been thinking about trying primer to prep it but i'm not sure if thats a good idea. any tips are welcome, thank you.