You've got good advice so far. I've done a lot of work on an excavator and own one. Using it is not rocket science. I think it took me a less than a day to get cocky and think I knew how to use a machine and probably a month or more to know how to use it SAFELY under all circumstances.
As someone who's worked machines on my own land, roadways and building sites, I am amazed that hire companies will still hire a machine to someone with absolutely no training. You wouldn't be let near a building site without the right qualifications, etc. A relative of mine had a trip via air ambulance for emergency treatment after hiring a machine and getting crushed when he tipped it over. I asked him why on earth he hadn't asked me to do the work (I'd have done it for transport & fuel costs). He said that he'd seen me operate a machine, "how difficult could it be?". Anyway, thanks to the NHS and 12 weeks recuperation he was fine.
Minis are IMO just as dangerous than the larger machines, they are easier to tip over and the boom of a 1.5tonne mini will kill you just as stone dead as a big machine if you get in the way.
If I ruled the world, there would be MINIMUM 1 day training + exam pass on safety awareness & safe digging practice before you could hire a machine.