How can an inexperienced pilot tell if the weather is good enough for flying?
I'm a UK PPL of 14 years, I fly out of North Weald which is on the opposite side on London to Farnborough, so I'm well placed to give you some tips here. First, use the Met Office aviation portal for your planning, most of the services a PPL will use are free. Metars are useless for planning as they only say how the weather is right now, TAFs are good for planning, however they only get you so far as they show you the forecast for one location. The Met Office portal gives you access to the low level forecast charts and spot wind charts, these give the big picture for the whole UK and Europe, including fronts, and forecasts in specific zones. These are published 4 times a day and are good for about 18 hours each.

The weather in the south east of England is very hard to predict accurately, it's getting better as they throw more computing power at it but it's still a challenge. When I do my weather planning I look at the low level chart and spot winds, then I look at the TAFs throughout the area. Heathrow and Gatwick both have 24 hour TAFs, and Farnborough is snuggled between them I'd look at them both and assume the worst from each. 

Read the TAFs and look at the briefing charts every day you can until you get a feel for it, experience will give you confidence. 

Next set limits. In the SE of England there ain't much topography but you don't want to cruise below 800ft in most places, back before I got an instrument rating I typically set a limit of 1000 ft ceiling, anything below and I wouldn't fly except for circuits, and even than that's pushing it. Wind-wise you need to know your crosswind limit for your airplane and yourself. It doesn't matter if your airplane's rated for 20 knots if you can't hack it, so don't put yourself in a bad position. 

Lastly, UK TAFs have a funny quirk. You'll often see PROB for probability in a TAF. The only 2 figures you'll ever see in a UK TAF are PROB 30 and PROB 40, the numbers are for percentage likelihood. PROB 30 means it's unlikely to happen, whereas PROB 40 means it probably will happen. In other words a 40% probability does not mean 40%, but about 60-70%, don't ask me why. So if you see PROB 40 consider it likely.