Time Travel in any usable capacity will probably never happen. And honestly, we're all time travellers -- all moving forward. But not backward.
If I fell asleep tonight and woke up in 1986, would I track down my past self -- 9 years old at that point -- and attempt to impart some wisdom? How would my past self react? What if tomorrow I bumped into my future self on the street and he started babbling about the Future? Would I write him off as insane? Fortunately, I'll never really have to answer that question but I'd probably at least hear him out, provided he could convince me that he was, in fact, from the future and was actually my future self.
That part's easy. All I need to do it think of a phrase now and earmark it for use if I ever run into my past self. The me in the future will also have knowledge of that phrase and be able to convince the current me on the spot that he's a future version of me. If that makes sense.
The only time travel we have access to is our memory and documentation, like photos and diary entries. I can flip open an old piece of writing or flip through old photos and be "in that moment." Pictures are really good for that, at least for me.
I'll be the first to admit that I tend to wallow in the Past like a pig in filth. I like to remember "How things were" rather than thinking about "What things will come." And it's to my detriment -- and by extension, my family's -- that I do this. I'm really making an effort to not wrap myself in layers of nostalgia but it can be pretty damn tough.
That's probably what wisdom I'd try to impart on my 9-year old self: Live in the now, prepare for the future, and think fondly on the past but don't wallow in it.