What is the best advice you have ever given someone?

I'm not sure what's the best piece of advice I've given someone but one that I received by a successful founder and now give to others is..

"Be aware of well-intended, bad advice." 

Everyone's' situation, role, company, etc. is different. Just because there is a someone genuinely trying to help you doesn't mean it's always the right thing for you to do.

Find a job that matches your passion... if you're not there yet, don't be afraid to shift and even downgrade your level to get you to that career path that aligns with your passion.  

Give more than you get

Be kind and take no short cuts. Additionally never stop learning.

Remember that you teach people how you want to be treated.