What's the best advice you've received!?

Take the time to understand the purpose of each workout

"Pretend you're pinching a coin between your butt cheeks"

(swim advice)

Your biggest limiter is your own brain

^^^  Winner.  </thread> 

Find a Masters group and (attempt to) swim with them.

More people should do this, plus strive to understand how each session relates to the sessions a few days before and after.  Also, don't be afraid to change the planned session if the intended purpose isn't appropriate now.  ie:  don't do the hard intervals that were scheduled if you only got 4 hours of sleep the night before.

Do your own race. Don't worry about anyone else.

I got this during the build part of Ironman training where I just felt so slow and crap at all the sports. I took it and made the day into 'my Ironman Day' that was specifically for me. I ended up executing my race plan very well and my result was better than I had anticipated! 

This.  Make sure you're enjoying it.  Otherwise what's the point?

Ironman race advice:

Keep going. You will be tired. Just keep going.

shut up and listen

After "Don't quit your day job":

Be consistent with your training.  Otherwise you're starting over all the time.

Mark

Yes, mine is a variation of this - "understand the key part of each workout and make sure to accomplish it". 

If it's supposed to be a 30 minute run with intervals in the middle (10 min warmup, 5 x (2 min hard, 1 min easy), cooldown) and you just run T2 for 30 minutes, you can say you did your workout, but you didn't do your workout.  You did something else.

Same for say the long run or long bike.  The actual training part - the overload part, the part that forces adaptation during recovery - is the last few miles of the workout.  If you short that, or go out hard and fade and phone in the last few miles, then you again didn't do the workout you do something else.

"Every day do something to help someone.  If you do this, you will always be happy".  - my Grandpa