Microcosmic
Orbit
Opening All of the Channels
Classic pictures of acupoints of the conception and governor vessels.
Opening
the Channels: It's much more complex than you might think.
The microcosmic orbit is important, but it's not a panacea. There are many channels in Chinese medicine, and they all work together (along with every other aspect of the body).
That's the point of the holistic view: that the body is integral. You've
got to start somewhere, and it's not a bad thing to start learning about the
orbit, but don't mislead yourself with a simplistic orbit fantasy.
Even the orbit itself is not as simple as portrayed in the above pictures. I suggest that you look up du & ren in a book on Chinese medicine. The descriptions of the vessels' main trajectories and branches are considerably more complex. Then there's the rich study of acupoints and self-acupressure.
There's plenty to learn.
A version of the microcosmic that encompasses just the lower jiao.
Front Vessel First, Include Elixir Fields
The important, and under-utilized, front vessel. Gently manipulating the tan tiens to facilitate flow and balance through the orbit.
Orbit Physical Work
Many beginners focus mostly on the meditations, and
often don't realize how physically
integral the orbit is. Most live instruction includes moving qi gong
exercises that work with the orbit on a very physical level - obviously way beyond the scope of this website.
Short of that, general exercise and some of the following might help:
Adjacent to the topic of du (the governor vessel): spine marrow-washing and the key role of the sacrum.
Winner in the category of "simplest, most effective and most surprisingly under-utilized" method. :)
Part of a short series of massage essays.
Confluent Acupoints of the 8 Extraordinary Vessels
Easy-to-reach acupoints for activating all 8 extraordinary vessels.
Lower Tan Tien Breathing while in a Bridge
Very helpful for opening up the belly. Some guys really consider this a staple for opening up ren (the front channel of the orbit) and for loosening bound up sexual tension from the lower tan tien. .. As well as, obviously, articulating the - very important - spine.

Heaven and Earth: the macrocosmic
Inclusion of legs and earth is not optional, but absolutely necessary for healthy long term practice. If your orbit practice habituates you to feeling the lower crescent of the orbit to be "bottom", then you've disconnected from earth, sacrificed a fundamental that provides root and stability. A much more functional beginning physical orientation is toward the integration of the crown, perineum and soles of feet, not just the crown and perineum. It is the integration of heaven and earth through and with the body that provides balance, strength, harmony. Your tan tien should feel both.

(Oh!, yeah... both the leg and arm routes are part of the macrocosmic.)
Emphasis of the Core Vessel: the Tao
Of the eight extraordinary vessels, the microcosmic orbit (du & ren) sometimes garners the most press, attention, emphasis. That emphasis is mis-placed, as the more critical transformations of alchemy occur within the deep-centers, which reside along the core vessel (a.k.a. central vessel). This doesn't mean that the m.orbit isn't important, nor that all of the eight extraordinaries aren't important, only that correct emphasis is sometimes lost.

don't mislead yourself with a simplistic orbit fantasy.
for long term, balanced, thorough, healthy progress
gradually open all of the channels.