Know Thyself !

[Admin]

Or the expanded version, simple saying # 3:

Make yourself a better person and know who you are before you try and know someone else and expect them to know you.

[BC]

Other versions (if I correctly caught the drift):

You can't do another person any bit of good if you ain't got it together yourself.

If you can't follow your own advice, don't expect anyone else to..

The weakest link in the chain is always 'Me'.

It's quite ok to dot the 'i's' but don't start a sentence with it.

[ScottinCrimea]

How can you explain yourself to another person if you don't know who you are?

[Faux Pas]

If you don't know where you've been, how do you know where you're going

[steviej]

Boxing is a lot like ballet except there's no choreography and the dancers hit each other ....