After a while when you have mastered the easier puzzles and have solved a few killer puzzles you will find that you will want to learn how to solve sudoku faster and probably spend some time practicing the more advanced strategies. Now many people may say that they have a killer sudoku tip you can use to really speed up your solving speeds. But really to get fast at sudoku you need to keep solving more and more puzzles.
Speed comes with practice, first you should try to just solve a puzzle correctly without worrying about how long it takes. If it takes you much longer than normal that's ok, Just keep working the puzzles and you will find that over time your solving speed gets better and better.
Now there are some more advanced strategies you can use that will help you fill in any missing cells that you are trying to figure out. If you have already mastered the more basic tips take some time to learn the advanced tactics and apply them to your puzzles.