Accentuate the positive
eliminate the negative.
Step 1. Work out what crimes your police force are good at solving.
Step 2. Create more offences in those categories
Step 3. Put up barriers to reporting, for crimes you're not good at solving (or that are too hard, expensive, unglamorous), so they don't get reported - see step 4.
Step 4. Reorganise the way crime figures are reported. Say, into 3 groups: reported, recorded and detected
Step 5. Choose whichever of these groups shows the biggest improvement, claim this is the most relevant measurement.
Step 6. Praise your officers for doing such a good job at reducing crime.
Step 7. At the same time you're saying crime is at it's lowest for years, claim there are new, hidden threats that mean you need even more officers
Step 8. Instigate a process of continual improvement, so it's impossible to compare current and past performance as the rules get changed too frequently.