There are SO many different reasons why your electrics might be tripping but some common issues are below along with some home remedies. 

1. If you've recently had some electrical work carried out such as additional sockets or switches then there's a chance a cable may have got damaged when the sockets were being screwed back. After a bit of use plugging things in the cables will move ever so slightly which could then cause 2 cables to short out tripping the electrics so if you've had some additional sockets other electrical work carried out in your home recently then inspecting them would be a good place to start. 

2. Water and electricity don't mix and water ingress is a common issue when it comes to tripping electrics. Rubber seals on outdoor sockets and joint boxes eventually fail or get damaged and their IP rating becomes defunct and allows water in to the unit. Poor installation of the accessories can also cause water ingress. If your electrics are tripping it would be a good idea to isolate any outdoor sockets, lights, pond pumps etc before trying to turn the power back on. 

3. Earth leakage occurs naturally on every installation and if you only have 1 RCD protecting a number of circuits, the cumulative earth leakage could be enough to topple the RCD seemingly at completely random times. Earth leakage becomes worse as the insulation around your cables degrade over 30+ years. Any items with electrical components such as PCB's, LED lights, digital displays, computers, heating elements, fridge freezer compressors  etc will all give off earth leakage when in use. If your electrics are tripping at random it would be wise get a registered electrician out to test how much earth leakage there is on your installation.