When cloning marijuana plants, it's important to have a very controlled environment, which means good air conditioning, thermostats, heat mats, and measuring instruments. Then, you can maintain your settings within a certain range at all times. If, for example, your clone room temperature had a range of more than 10 degrees from day to night or season to season, you'd probably run into some consistency problems with your rooting and cannabis clone health.
For small-scale operations, you don't need to be great at cloning to have success- you just have to cut a lot more clones than you need. Some will root and some won't, but you'll get enough. Also, with small-scale setups, clone machines can be used. These are essentially little enclosed hydroponic units that maintain good consistency of humidity, oxygen, and moisture in the medium during the incubation process.
For large-scale operations, any loss or slow down in production means less company income, and that needs to get fixed. Many possible little tweaks can be made to the system in order to improve it. Even something as minute as using a level to balance your incubating clone trays, so water doesn't move downhill and distribute itself unevenly, can make a difference.
Start by getting your ambient room temperature set for the smallest 24-hour range possible. Then, do the same with your heat mat thermostats. After that, it's all about water balance, including the humidity inside the propagation dome and the moisture of the medium that holds the cuttings. All of these properties are the most critical for success.
You can learn how to clone cannabis by paying attention to and controlling these things, plus doing experiments of your own, and over time, your success rate will keep getting higher. Just stay with it, and measure as many things as possible.
And you need any help, just ask ;)