Hello Milly. There are a few related posts on this forum where I've offered my opinion on this matter. The most recent one I could find is here. I can never quite find the right words to discuss this matter without seeming somewhat confrontational - but basically I don't believe in this kind of transference and thinking about it in the terms that get tossed around by many practitioners leads to far more detriment (for them and their patients) than any kind of good. Giving out "too much" energy, taking in "evil qi" - all of these are quite negative in many ways and show a poor understanding of what is (and isn't) happening when working on other people. A recent study, for example, found that just by looking at someone who is sick your immune system is activated - imagine what happens when you throw in working directly with them and on top of that some altruism.... Nothing bad assuredly.
All that said, this type of work is physically, emotionally and mentally demanding - much more so than many think initially. Because of this I always recommend the daily practice of tai chi and/or qi gong (certainly more so than meditation, yoga, running, whatever). Nothing against any other self-help/exercise tool but tai chi and qi gong not only build your personal reservoir of qi but they increase your sensitivity to energy (both in "issuing" and in what you may be receiving). Essentially if your personal energy is strong and your sensitivity is well cultivated the whole good energy/bad energy argument becomes a mute point.
On the physical side, obviously correct form and technique is crucial, starting slow and working up slowly so your body can develop correctly. In China many of the tuina massage practitioners spent years cultivating their own energy, understanding theory, and working their muscles through various exercises, massaging rice bags, etc. until they were even allowed to touch a patient. As our schools are setup to get you working as quickly as possible we are obviously missing out on much of this. As someone who plans to practice for a long period of time, then, taking some of this development work upon yourself is important.
For Tai Chi and Qi Gong training I would suggest you look locally for a practitioner as that is best. Qi gong routines are generally easier to learn than Tai Chi (although there are short forms), our tai chi/qi gong section has a number of books and dvds. On the qi gong side I am partial to the Da Peng Gong and on the Tai Chi side the 12 movement yang style form would be a good place to start (in DVD) if you cannot find a teacher locally.