I am asked this question a lot and the answer, most of the time is sadly, no.
I was fortunate to enter this field and be trained by some very high level people who had the time and resource to guide me through the early stages until I became competent in my own right.
These days I do not have the time to train someone up in this way and therefore would only consider applications from those with previous experience in the field.
I do not work alone. I do call upon others with very specialized backgrounds who assist me as and when necessary. All I need to do is brief them on the job and they are immediately ready to go.
A good example is mobile surveillance. That is a surveillance involving cars rather than one undertaken on foot. I was taught to do this by an instructor that trained the Police in the Thames Valley area in the UK, many years ago. As vehicle surveillance is very dangerous and involves a huge amount of skill even when speed is not involved, not only does one have to employ advanced driving techniques that must have been taught by a professional, but it is also necessary to keep up a running commentary to others involved in the surveillance using a particular language that leaves no room for misunderstanding and therefore errors. This is the ultimate in multitasking as your attention can not be focussed on just one thing but must be on many things and all at the same level and that level must be high enough to never endanger the lives of others.
Even on foot, following someone is not easy and those who are not professionals tend to stand in the wrong place, in the worng position at the wrong time and thus their cover is blown straight away.