first off the most important thing is to make sure that your computer is running at peak performance. There are software packages out there that will do it for you automatically, I recommend AVG pc tuneup. Second, make sure that your resource pack is not HD, if you use one that is. I recommend using the minecraft default to verify that everything else is working. Third, make sure that you have the most updated version of java for your computer. Fourth, check your task manager and make sure that there isn't any programs running that shouldn't be. If after all that you are still having issues, then it might be time to get your computer into a shop to either get upgraded or tweaked out...
-Frobuzmumber
