Time travel is tricky.
After all, you've got a character from the present, past, or future and you're sending them into another time period. If you're sending them into the past, they're going to know what happens (vaguely) for important events. They're also going to think of things like speech patterns, slang, and dress code as archaic. Their attitudes will differ from the people natural to those times. While they might be able to fit in (depending on their familiarity with history), there will be many differences between the culture they know and the culture they are thrust into.
Not to mention the small problem of time itself. If they're going back in time, they can't mess around with the outcomes of history, etc. or they might prevent themselves from being born. Most books remedy this with a loop -- the main character going back in time then becomes his/her own ancestor, thus s/he needs to go back in time in the first place.
However, going forward in time eliminates this problem. They can't rewrite history because they don't know what it is. They will only rewrite the ambiguous concept known as the future (and we all know that isn't written in stone).
But going forward in time creates its own set of problems. After all, the adjusting period is much more exaggerated for someone who has no idea what to expect. Learning what became of friends, relatives, etc. might be disturbing to the character. Not to mention the culture shock they would get.
For a writer, it is easiest to take what is known and extrapolate. So moving a character from the past to the present or from the present to the past is easy. Moving a character from the present to the future -- not so much.
Like in alternate history, you have to think about what sorts of events might have brought us to whatever future you create. You're building a new world, a new culture, as surely as if you were creating another dimension. If you're wondering where to start, take a look at my world building blog mini-series here.