1. Understand the value of your service, and the problems it will solve.
How is this service going to build wealth, profit or cashflow? Or, will it free up time and reduce stress for your client?
Remember the Three Freedoms: Financial, Time and Mind.
2. Believe in your value and back yourself.
You have the skills and experience to help, no-one knows your clients' financial situation better than you do. If you lack confidence, it's time to build it.
3. Articulate this value and stop speaking 'Accountanese.' Use language that helps your clients understand WIIFM ('what's in it for me?').
4. Ask for the order - state your price and shut up! It sounds blunt but your client will either accept or decline your proposal. If they decline, it's because their perception of the value you are offering doesn't outweigh the price (see point 1). In this case you can ask them how they propose to solve the problems you've identified.
If a client declines, this is their choice; don't push, and remember, 'no' isn't necessarily 'never.'
5. You must learn how to sell.
Your clients need these services, but they're not going to line up to buy them; unlike compliance - they aren't compulsory. Selling is an acquired skill, so get the training and support you need - just as you have on the technical aspects of your role.