1) Know your business enivronement. Study the business.  Understand how the business operates and how it makes money.  What are the most prominent business processes within the business. What systems does the business have in place today to help support their processes.

2) Don't underestimate the importance of outstanding business requirements.  Even mediocre business requirements cost projects a lot of money as they carry over to each successive phase of the project.

• Document WHAT the business needs not HOW
  
• Document the WHY, or the business rationale behind the requirement.  As analysts get deep into the system design, question arise about why a requirement is stated a certain way.  The rationale helps answer these question.  Often by this put the business has forgotten WHY they said they needed something
  
• Also take a look at the ModernAnalyst interview questions on the characteristics of a good requirement ;-)

3) Always think in terms of the logical and the physical design separately.  Model the system from a logical perspective first, then get into the physical design.  This is probably the MOST difficult thing for developers transitioning to a business analyst role.  I've witnessed their challenges in this ara first hand.  Both the logical and physical design are important, but they should be separate and distinct.   The logical design will align more closely with the business needs and won't change as frequently.  The physical design may change based on architectural constraints and other systems that it needs to interface with.

4)  Study and understand the importance and benefits of:

• a Fact Model (also sometimes call a Business Entity Model)
  
• a Logical Data Dictionary.
  

I'll let you do the research (some can be found here on ModernAnalyst.com).  Which leads into the next point...


5) Don't be a lazy analyst.  Most analyst think that learning and career growth is whatever happens between 9am and 5pm.  The best analysts regularly study and read up on business analysis tools, concepts, methodologies, etc., outside of their regular work hours.  Everybody wants to think they are the top 20% of BAs out there.  Well 80% of them are WRONG.  To be in the top 20% takes real effort.  If you are on this site frequently, you are already taking the first steps that many BAs don't.

Good Luck!!