I cannot state this enough, RTFM
Once that is done, read this too:
Most of the time beginners encounter performance issues, it's an easy fix and is mainly due to a lack of understanding of how the engine works.
I'm not saying that you should dive head first in the runtime code for C2 and C3 (even though, if you can, you probably should do it because it's fun), but to at least read the resources that have been provided to you by the people who wrote the software. And by "people who wrote the software", I mean Ashley because all of these articles are super old but still relevant today.
Finally, I'm absolutely not the first dude from the community to give performance tips, so you should probably spend some time reading these as well:
(Please note that these were made for C2, before C3 was even revealed and should be read with that in mind if you're using C3)
mega.nz (this e-book contains info about the dead IntelXDK service. Just ignore that part)