As you become familiar with different types of work you start to see similar principles for each.  The layout of threads on a screw are no different from stair steps.  The flow of liquid  in a closed hydraulic system is  like electricity.

 The most important thing that a handyman has is an objective view of his skills.  He must know what it is ok to tackle..  Sure anybody can do anything as long as there is enough time.  But realistically   he should attend to projects that can be finished with a minimun  of learining time.  Some jobs require a lot of reasearching before they can even be atteimpted and you can't expect  your client to pay for your schooling.

A handyman must use the experts adivce and the best way to get that is to simply ask for it and when you do ask  for advice let your  ego be gone and  do not pretend  to know anything about the subject you are reasearching...Most people take pride in the expertise they will gladly tell you the ins and outs of  their trade if you  just listen intently and show them  that they are the expert.  Dont be tempted to throw in the little bits and pieces of information you have. about a particular trade.  Just listen and every once a while say something like"I never would a thought of that" Or "How about that?"