Here's something to avoid: re-reading old diaries. Resist the urge. You will a) be depressed at how little you've changed and b) be depressed at how obvious the warning signs are about everything that will go wrong in the coming months and years.
Or maybe that's just me.
Now, I have changed quite a bit, to be fair. I'm not nearly as depressed as I used to be--years of medication and counseling have made me more resilient, better able to draw on my coping resources, including good friends.
Tomorrow's advice: do not save cards given to you by your partner/lover/spouse. Just don't. At some point you'll either a) have a massive pile of cards that say little about your lives together, and/or b) have to throw them out, and will be tempted to--yes, you guessed it--read them.