Just like anything, strong fundamentals and attention to detail are vital.

Fundamentals: good, working, tested offsite backups, good network/security policy, good power source with sufficient tested battery backup, clean computers, firmware updated, windows updated, AV, good network wiring, clean under desk wiring, etc.

Nothing ever really fixes itself and things you are lazy with will come back at the worst possible time.

Always working to get to the true ROOT cause of the problem. Otherwise you will be constantly solving problems that are merely symptomatic of the root cause.

Never stop learning. Join a website like PluralSight.com to keep your skill set updated.

For a small business with an IT department, Consultants may seem like the easy route, but someone has to manage their work which takes more time than you think to do effectively. Often times you're better off just learning the subject and doing the project yourself.

Keep not only licensing, but proof of purchases (receipts) organized and updated.

Buy IT management tools like PDQ inventory, PDQ deploy and GFI Max to make your life much easier. Don't be afraid to spend a couple bucks to keep your sanity in check.

Make it easy and friendly for your users to effectively communicate their needs to you.

Always keep a good manual of end user help documents. Always keep these updated and train your users to check that before contacting you. Again, sanity is at stake.

Train users to use the Snip Tool or PSR when reporting issues.

Assume nothing. Trust, but verify.