thank you both - have looked at the site but it doesn't really help as I want to know how to solve the puzzle. It would probably help once I had finished to check
I look at 3 lines at a time for where there are 2 numbers same, so if 7 in Line 1 and 2 but not in 3, then see where it can be in that line. I keep doing that to work out the ones that only have one option. As the lines fill up a bit I check out numbers still to appear in that line to see is any have only one correct location. Then I start looking in each square to see if any of the missing numbers only have one place that works
I do a lot (or at least used to) of sudokus and would suggest that Grasscarp's method is the way to start. Have looked over Chrissa's suggestion and have to say that ( unless for the prize very difficult ones), you should be able to solve without going into such detail. Good luck.
I start by filling in as many 1's then 2's, 3's etc. Then repeat as you will possibly fill in available spaces as you go. Then do lines or 3x3 squares. As a beginner, I would start with easy sudoku's and build up the difficulty, the more you do the 'easier' they become and you will get a system that suits you.