1.  Your understanding of reactions - transformation plus any regiochemistry and stereochemistry issues and mechanisms.
2.  How reactions and functional group interconversions are inter-related.

The most common reasons for students to struggle with these questions are:

• Do not know the reactions well enough
  
• Poor problem solving skills (e.g. logic, miss reading the question)
• Lack of attention to detail (e.g. counting carbon atoms)
• Poor basic chemistry skills (e.g. nomenclature)

Is there a good way to try to solve such a question ?   YES, use the disconnection approach

Work backwards from the molecule you are trying to make towards the allowed starting materials.
If the compound is given as a name, first DRAW out the structure.

With the structure...

1. identify the functional group or groups present
2. identify the reactions you can use to make that functional group
3. break bonds that correspond reactions (remember reactions happen at or near functional groups)
4. repeat the steps 1-3 working back to the starting materials.
   

More information on the disconnection approach?

DON'T  TRY TO PICK A STARTING MATERIAL AND WORK FORWARD FROM THERE.  It is often an ineffective and inefficient way to get a good answer. It may work for simple (i.e. short) problems, but it will not be effective in more complex problems.