It is always a good idea to try and get feedback about not only your products and services but your business as a whole in terms of customer service, pricing etc. Another item you should try and get feedback on is your website. It may be that your website is used as a portfolio or possibly that it is ecommerce and you are selling products directly from it. Either way, asking your customer how they found your site and whether there is anything additional that they would like to see on it is vital to making improvements.
Some businesses send out emails to clients following a purchase from their site asking about their experience, but many customers do not reply to this. Ideally you need to make sure that any feedback request is sent at the correct time and is very easy for your customer to complete. If the questionnaire takes too long no one will bother, it is better to get a small amount of feedback from a number of people than no feedback at all. If you are able to offer a reward (such as a discount on future purchases) for completing a survey or feedback form then you are likely to receive more information back.
When you gather together your information be sure to use this in your marketing going forward. If for example, you add a new feature to your website that has been requested by your customers be sure to promote this and state that you have listen to what the people want.