It is always best to try and find a childminder through personal recommendation, so ask everyone you know in the area who has children. If you are new to the area you may need to go through the more official channlels, and a good place to start is a government backed organization like Childcare.co.uk. They have 95 registered childminders, and if you put your postcode in the search box you can find a list of people near your home.
Having narrowed down the search, you should look at the ratings given to individual childminders and see if you can get in touch with any local parents who use their services. If you aren't able to get any independent recommendations you should try and meet the childminder to make your own assessment. For this, you may find this page helpful - in particular, you could look at the list of questions to ask.