very dirty, very dusty. The electrician should not use a grit and dust generating machine wall chasing machine except in an empty house. Make sure he agrees this in advance. You will have to move a lot of furniture and carpets. The dust will get into everything. Buy a canister vac from a DIY supplier, with a spare cartidge filter and some accessory bags, and hide or dismantle your domestic hoover as the fine dust will clog or damage it. The dust will also damage PCs, TVs and other electronic devices unless they are sealed up until the work is finished and the house has been fully cleaned. It will get into clothes in drawers and wardrobes too.
You can expect to need to redecorate throughout.
Get used to the idea that some of your floors will have to come up, even if they have been newly tiled or laminated.
Go round the house with the electrician and a felt-tip pen and mark on the walls where you want all the switches and sockets to go before he starts work. It will be much easier and cheaper to do the plan before the work, rather than the other way round. Have more sockets than you think you could possibly need, especially in the kitchen. Ask what the price difference will be if you have RCBOs (they are worth having if money is not too tight) especially on the freezer circuit.
Be aware that there is no reason to suppose that a good electrician will also be a good plasterer, and make other arrangements.