All good advice from Ericmark I would add;
1. consider how many sockets you require particularly the kitchen and where you are likely to place your home entertainment system.
For example if you have 4 work top appliances in the kitchen then consider having 4 2 gang sockets
Home entertainment systems, we have a bank of 4 2gang bouble sockets
2. The master bedroom or bedrooms, as my wife could not decide where she wanted the bed I placed 2 gang sockets either side of the bed width where ever I thought she may wish to have the bed, it has been fool proof since!!!
3. Think about everything you might want, i.e. outside sockets, lights etc and have these put in even if you are not going to use them right away.
4. Down lighters - Mmmm not popular with us sparks. I tend to go toward 240v fittings as low voltage fittings have transformers and they are renowned for breaking, you can fit the 240v with low voltage of led.
Plan what you want and talk it through with your sparks, get a few quotes and check them out at
www.competentperson.co.uk