My method is to mark the consequences of guesses with a light dot above the number. If a contradiction is found it is then easy to erase all the dots and go back to the original guess.

After filling in all the numbers I can deduce without guessing, I lightly fill in every remaining box with all the possible numbers. Now to make a guess I pick one number and mark it with a light dot above it. Then continue, using standard methods to find other numbers, marking all these new numbers with dots. Hopefully one can continue on to either a solution or a contradiction. If the latter, you then erase all the dots and remove the originally-guessed number that's turned out to be impossible.

First I fill in all the numbers I can using standard logic methods. Then I lightly fill in every remaining box with all the possible numbers. Now look for a two boxes in the same row or column with matching pairs such as 2,3 and 2,3. I pick one number,say 2, and mark it with a light dot above it. Then continue, using standard methods to find other numbers, marking all these new numbers with dots. Hopefully one can continue on to either a solution or a contradiction. If the latter, you then erase all the dots and go back to the original ‘guess’ 2 and write this in as a known number. Then I continue on using this new number. Perhaps a second guess is needed to advance. An even better guess is to perhaps find a triple of pairs in a row or column e.g. (2,5),(2,8),(5,8) and pick one number and get two others to continue as before.

My method is to mark the consequences of guesses with a light dot above the number. If a contradiction is found it is then easy to erase all the dots and go back to the original guess.