Read the instructions carefully. Be prepared for some surprise element. 

First scan though the whole paper and notice if there are any type of questions having too many marks etc.

Start from the first question and keep on doing the ones that you are able to do. Do not get emotionally attached to a question if it may take too long. Make a note of some questions which you consider worthwhile trying again (you may use pencil mark if it is allowed). Finish the paper at one go like this and then look at the questions on which you had left marks.

Do not ignore any subject in the paper.