Is there anything to avoid with meridians? For example, running them backwards all at once, sedating heart, governing, central, etc.?
This is an important question. Do not flush or sedate heart meridian. Rarely sedate spleen meridian. There are "forbidden points" in Chinese Medicine, such as points that are never to be used with a woman who is pregnant. Practitioners should be familiar with these constraints. They are usually listed on the standard acupuncture charts available from schools of acupuncture.
But there is another level of answer to this question, which is simply to stay alert for how the client responds as the work unfolds. Energy interventions give immediate feedback, and they are also quite forgiving. You can energy test the results of an intervention when you are unsure, and you can do the opposite procedure (such as strengthening a meridian you have sedated) to "undo" an intervention.