Speak to the neighbours & people walking around nearby, just be honest and tell them you’re thinking of living nearby and if they’ve got any advice or can they tell you what the area is like, any problems they’ve had etc.
Speak with local shop keepers / staff and ask about the area, obviously don’t do this if there is a big queue behind you so find a quiet time to do it.
Visit the property at various times of the day / week. For instance, when we were buying a our first home, we went and visited on Friday & Saturday nights, then again mid-week and an hour or so after schools finished. Just park up for 10-15 minutes, turn off the engine and see/listen to what is happening (if anything), yes it sounds strange but remember you will be spending potentially many years living somewhere so it’s best to know in advance if there are going to be problems. Also go for local walks from the property, walking to the local pubs/parks/shops etc.
Check the postcode on Check My File http://www.checkmyfile.com/postcode-check/SW1A-2AA.htm – It will give you a rough credit score for people living in this area. This can help you gauge the sort of people you will be living near (+ more important if your insurances will increase).
Using Street View and clicking this icon to see how the area/property has changed over time
Get a quote for car insurance, if your car insurance dramatically increases then this could indicate the area isn’t safe or has problems.
Pull up Google Street view and have a virtual drive around the area, you can pick up all sorts from: people having arguments in the street to rubbish piling up around the back, it also helps you check the difference over the years by pressing this icon (see photo).
Ask local people on forums, selling groups etc.
Don’t rely just on the internet, if you’re buying a house then it is worth doing a full survey (costing £400-£700) these can seriously save your bacon longterm, often it’s best to find a local company who knows the area well.