One part of my theory of time travel is you can't jump forward in time. A person already moves forward in time every second of every day, and the only time a person could ever move forward in time at a faster pace would be if they moved at really, really high speeds. But then everyone they know just ages faster while that person is gone, and since that person is gone, there is no chance of meeting their 'future self' since they weren't there to become their future self.
Another reason why jumping forward in time wouldn't work would be because the future doesn't exist yet. Every second of every day, people are faced with choices they could make that paves an ongoing path, making the future a reality by turning it into the present. People can speculate about the future by considering the consequences of actions they could carry out, but until they make a decision, the future is not solid and does not exist yet.
The past, however, does exist and is solid. If someone had the power to travel through time, then the only way they could travel would be backward. It would take a while to type down everything I have going on in my head, so here's a picture I drew on my tablet:
...If...I can...get it to work... Hold on! I almost got it! It's coming! XD