Ask around and see if any are recommended. Check their Ofsted reports - you can do this by going onto the Ofsted website and going into 'inspections', choose the primary school option on the left then put your postcode in. Also ask to see their most recent Sats results - your LEA should be able to provide you with these.
Also, health visitors usually can advise on schools.
Visit the school too - you will know straight away whether it 'feels right' for you and your child. My son was refused 1st choice this year and I visited another - hated it from the word go . Didn't feel right at all. You also need to consider which high school they feed into - I know it seems a long way off, but I checked the reports and results for those too before I made my decision.