I do this once in awhile and it's always a nice surprise to wake up one morning and find a message I wrote myself years ago.
When I get anything that I believe is from God, with a date on it or a time frame attached, I know I might not be cognizant enough to read back through my journal at the right time to get it. I've put notes on the fridge where it stays in front of me the whole time and I become oblivious to after awhile, but technology became my friend somewhere along the way.
I woke up the day after the last blood moon (no, I didn't really think it meant what everybody said) with a note in my inbox telling me that everything was changing and the old season had passed. It had more to say of course and was very exciting and I quickly saw the evidence. This happened through my built in email provider's reminder service. I use Yahoo, but Google has one as well, and I'm sure most others.
Future Me is a free service that lets you write a letter to yourself. If you go that route, make sure you verify your address and add them to your contacts so the email doesn't go to spam.
If you are fickle about staying with the same email company, this might not work for you. Definitely have it sent to a web based email like Gmail rather than something connected to your work, your college, or your ISP. For things far off, I would diversify and use more than one way to get your message across.
If you feel like you'll keep the same phone number, and especially if you like the idea of calling and talking to Future You, you can use ReminderGuru.
For the short term, and action oriented, sometimes I put them on todoist, which is my to do list app. You can list tasks with a due date on them and they will pop up on that date. On Sept 8, "Mess with the monkey" popped up. (Why does it always have to be so cryptic?) That one turned out to be about confronting a mocking spirit.
So I'm going to pretend you're all in my class and give you an assignment assuming you already know how to prophesy. If you don't, or you need to build up more confidence, I highly recommend this class.)
Your job is to ask God for something good to know 3 years from now and schedule it to be sent to Future You. You can do any time frame instead of 3 years, but that seemed far enough out that major change may have taken place and far enough out that you'll have forgotten all about this, yet not so far out that you have to wait forever. Far out man! Have fun with this!