When you do something you should do it as well as you can.
A journey of a thousand miles begins with a single step
To progress at anything, you first need to get started
The journey is the reward
The most valuable, fulfilling and exciting part of achieving something is the work and effort put into the endeavour
Jack of all trades and master of none
Is a person who can do almost anything, but he rarely excels in any of them.
Jam tomorrow and jam yesterday, but never jam today
What you early hope for does not seem to be happening
Judge not, lest ye be judged
Do not judge others as you are not perfect yourself, so be merciful in the hope that others will show you mercy one day
Jump from the frying pan into the fire
To go from a bad position to a worse one.