Welcome! It varies a lot, because different people have different needs and different aesthetics. You can get a lot of inspiration from other people’s project reports, though. 
First UK resources
There are two good threads you might want to start with, both specific to the UK.
The following is the UK lighting FAQ. Lighting control for the UK is quite different than for the US because there just aren’t the same number of wall switches available, and because many UK homes do not have a third wire (neutral) at the light switch. But there are still about a dozen different ways to provide lighting control.
Next, here’s a list where UK members discuss what they were doing in their own projects. It might give you some ideas.
Project Reports: The quick browse lists
Next, the community – created wiki has quick browse lists to help you find related threads in these forums.
I definitely suggest you look at the “get started” list in the project reports section. It’s true that many of those will refer to US devices, but they also tend to give more context for a project and that can help you decide if it’s something you might want to do, and then you can start your own thread in the projects section and ask for ideas on what devices available in the UK might accomplish something similar.
There are also threads under get started like “top 10 things to do at home automation” which again are less about devices and more about applications so apply to both regions.
In addition, the “impress your friends” list has some of the more unusual project ideas like a secret bookcase room. Those are just fun to read, although many of them have practical applications as well.
Household Composition
It will be helpful to those giving you specific suggestions about your own setup if you can tell us a little more about your intended goals. For example, if you are the only one in the home, then Projects like “light follows me” make a lot more sense than if, like one of our community members, you have eight kids.
We also talk a lot about the SAF or xAF factor. SAF stands for “spousal acceptance factor.” It can be quite easy to automate a home in a way that no one else can figure out how to get anything done! There was a scene on a recent television show where a person staying in a Home couldn’t figure out how to get up onto the bed as it was elevated considerably. Then the homeowner walked in and pressed a hidden button on the endframe and stairs came down from both sides of the bed. It was elegant and practical, but SAF was very low because it wasn’t intuitive. Light switches with a double tap or triple tap feature can have the same effect on a much smaller scale if other household members can’t figure out how to get the lights to turn off!
The main point is that home automation often has to satisfy more than just the The person who purchases and installs it. So many community members will have suggestions on how to increase usability for others.
(At my house, we use the term “xAF,” where the X stands for “anyone but me.” I have two housemates and we all have Friends and family who come to visit. I also have home health care workers. Not everyone has a smart phone, nor do I want to give account access to everyone. So my planning has to include thinking about all of the people who move through the home and how the automation features will work for them.)
Aesthetics
Also, aesthetics are a major issue for some community members while others are only concerned about the practical aspects. And people do vary in their aesthetics. For some people, a plastic button with glowing LEDs that can change color is very attractive. Others only want conventional looking devices. Still others want the kind of thing one might see at a luxury hotel – it’s fine if it has metal and LEDs, but it needs to look very posh. SAF can be a big factor here as well.
Budget
And then there’s budget. In my own case, my budget is about £200 per room, although I might go up to £400 for a room that had a television set up or a thermostat or some other specific use case that required special equipment. I don’t do every room, and I don’t necessarily do every switch even in the rooms that I do automate.
Other people might have a budget considerably higher, or somewhat lower. Or set a whole house budget of £1000 or less.
The point is just that different people will have very different budgets, and that does change the way in which a project might be done, and obviously how many projects might be done in a house.
So if you have any sense of what your own budget will be, that can also help others in giving you advice.