I will second Ken regarding his post. There is absolutely nothing to beat 'being on the job for real' AND spending the time with an experienced person.
I found that it helped dispel many of the romantic myths that may have been growing in my mind as well as giving me a firm handle on the whole process of the actual job being done.
eg: The setting up of equipment and pre-vacuuming etc can take a bit more time that you would initially expect. It also helps you understand the importance of being organised - as in knowing exactly how you are going to do the job - where you are going to leave your equipment etc. Little things like hoses and cables tend to suddenly play a new role in a live situation. You can't just let them snake about all over he floor and then hope that the client is NOT going to step on or trip over them.
They say that the devil is in the detail and I tend to agree. The 'big picture' may seem fine, but without the little things being organised, an otherwise fine job can turn into a complicated issue.
Best of luck for the future and remember, the harder you plan and organise, the luckier you get.