I guess the very first and most important piece of advice would be ALWAYS take your medicines as the doctor prescribes, every day....that seems so obvious, but many post-transplantees get to feeling comfortable and sometimes get lazy about meds and skipping a few times becomes once a week, then more and before you know it, the kidney is in trouble. Of course, we all have times when we forget our meds...just start taking them again and don't panic if you miss a dose.
Perhaps the second is your diet...eat lots of fruits and veggies if you are allowed, and don't forget whole grains and protein, dairy and lots of water if you aren't on a fluid restriction....I think I have to give a little credit for the longevity of my transplant to drinking water and lots of it! I like to fill some liter bottles with water and then chill them...you can drink out of them all through the day and if you ARE measuring fluid, you will know how much you have taken in.
Try to abstain from or limit alcohol and sugar...especially high fructose corn syrup found in soda and many other foods....I am a TOTAL fanatic about this! You have to read labels faithfully and see what is actually in the food you are consuming. Actually, new evidence has come out that high fructose corn syrup may cause chronic kidney failure, so I'd stay away from it as much as possible! High fructose corn syrup is hiding in almost everything! Bread, catsup, salad dressings, sauces, etc. all contain it but if you read labels, you can find products that are free of it....try and buy those if possible. I truly believe that high fructose corn syrup is POISON!
Always carry hand sanitizer gel in your purse, car, briefcase, etc. People may laugh, but they'll be the ones getting sick! LOL You touch so many things every day-germs are everywhere. When you get a cart at the supermarket, have some hand gel on a tissue and wipe the handle well....clean your hands before eating or even touching your face. You might want to carry a mask around in case you are "trapped" with a bunch of sick folks!

You don't have to get panicked about it, just be careful.
Wear sunscreen in the summer or if you are out in the sun for any length of time as transplant patients have a high incidence of skin cancer...see your dermatologist once a year. too. Keep all your doctor's appointments with your nephrologist and transplant doctor and go for all of that bloodwork even if you think you've become a human pincushion!
Of course, exercise, meeting with friends and just adopting a healthy lifestyle all around helps a lot....all things that are just good sense. Keep up with your hobbies and laugh a lot, too! Don't forget that your kidney was given to you so you could have a normal life and that includes having fun!
I also credit a lot to my faith in God and prayer....I know everyone doesn't feel this way, but it is something that I firmly believe has helped me. You have to decide if that is something that is right for you.
I don't really feel like I've given any advice that is new or surprising...just common sense stuff. You are now the owner of a new kidney that has been given to you as a gift...a second chance at life. Honor your donor by the way you take care of this gift and be a good steward of your health.
Take care of those beans!
Pam