My top three would be:

1) Build a team that supports you. Even a solopreneur needs a great team around them. Access to the right people at the right time is the key to staying out of trouble—accountants, lawyers, HR professionals, mentors, coaches, etc. Get used to group thinking problems. 

2) Know your numbers. The earlier you lean on data to direct your business decisions; the better off the business will be in the long run. Need help developing and analyzing the metrics unique to your business? Lean on people from item #1. 

3) Take time to fall in love with the journey. Arriving at a particular goal (destination) is fleeting. The minute you arrive "here," you immediately start planning to get "there." Focusing on attaining goals misses all the great moments along the way.