First of all, make sure your parts are designed to be CNC machining–friendly. For example, avoid features such as sharp corners, deep pockets, and thin walls.
Secondly, choose the right CNC machining company for your project. For simple and small parts, you can easily find small CNC machine shops that offer competitive pricing. However, if you need high-precision parts with complex geometries, a company like 6CProto — equipped with advanced multi-axis CNC mills, lathes, and full inspection facilities — would be a better fit.