I am building a web application which will store general details (address, email, landline....) about my company's clients.
What security measures should I put in place to comply with the Data Protection Act principles?
Is there anywhere a specific list of measure to put in place?
Sorry I forgot to mention In UK.
The way you've worded your question, it sounds like you are looking a checklist of security measures so you can say you comply with the DPA; in other words, some magic sauce that you can simply add to your application to make it compliant. I don't think that's a good way to proceed, because the DPA principles in general feed in to your business rules and (if required) your DPA registration.
First, understand what data it is you wish to process and how you will process it, in high-level terms. Only then should you start to sketch out your application's architecture; at that point, you will be well placed to think about the specific security measures you will need under Principle 7.