In the early days of my business, I did it all myself. I just cleaned the property in the same way as I cleaned my own house. If the carpets needed a clean then a hired a cleaner (you get these cleaners usually at the front door of homebase).
Now I am more established, I get cleaners in to do the jobs for me. Write down everything that you want them to do so no confusion. Get a couple of local cleaning companies out to have a look and go with who you feel most comfortable with.
I use a small local company and they do a good job for me. Didn't bother with any of the big named cleaning companies because at the end of the day, there is very little in the properties I have and certainly nothing valuable worth stealing.
Usually a clean for me will mean
Scrub the bathroom top to bottom including grout and tiles.
Same with Kitchen
Skirting boards
Windows
Carpets
Clean out fridge freezer
General dusting
It doesn't take that long when needed but I also say to my tenaants that if these jobs that I expect done (and were done for them moving in) are not then the cost of having a cleaner in to do it for them will be decucted from their deposit. It usually does work and everything is nice and clean.
Sorry for the big rambly post!