What are the mechanisms required for time travel?

I've just made a lot of things, i'd like to do again differently. Even thought it is impossible, I have all the time in the word and would like to pursue a quest for time travel. So just to get some external ideas, what do you think are the necessary factors/variable have been said to be need in order to control and/or travel in time? Please humour me if you're appalled in some sort.