I would rather provide thoughts about the reasoning of the usage of plasma weapons in general.
What if plasma weapons are inferior to projectile weapons and more expensive? They wouldn't be built and therefore never exist in a sci-fi world. A weapon which is destructive, has slow moving projectiles and is not lethal is of no real use on ground combat, unless causing injury and terror becomes a priority in future warfare - or policing.
Another consideration is that while plasma weapons are being developed, projectile weapons will also enjoy technological advancements. They could be able to fire around corners, have automated aim/aim assist, contain special payloads, etc. For large scale weaponry there are Gauss cannons and missiles.
So plasma weaponry has to be superior in at least many regards if you want it to be sufficiently often used.
For that they have to be either somewhat effective yet cheap to build, have immense destructive force in ground combat or have other advantages. They must be able to compete well enough against projectile weapons.
One example: Armors in general have been improved vastly, which render kinetic damage inferior. People in these armors (which became generic use) shrug of incoming hails of bullets and only suffer some recoil. Even if the area in which lethal injury occurs is heavily reduced, it's still worth it (as of lighter versions of such armor). The projectiles are either deflected or absorbed, but do not cause significant injuries. Explosive/kinetic damage may also be simply absorbed without too much trouble. However, the material used should be vulnerable to heat/plasma. But dismissing the protection from projectile weapons can never be afforded given what they would be capable of.
Plasma could however not only pierce such protection, but still be effective against unarmored targets. It would have to be able to pierce armor and the body covered by it.
Now, how it should occur is more technical and I will not go into that here. @Rowanas gave a good answer for that. My point is just that no matter what, it has to be able to compete well with projectile weapons in order to justify its existence. Why would aliens or humans use plasma weaponry if it wouldn't be better than projectiles? Just look at Star Wars - plenty of pew-pew weaponry with slowly moving shots, all of which could be deflected with light sabers. That's very badly thought-out. Mere WWII weapons would have been more effective.
The same goes for Star Gate - the Goa'uld only use energy weapons, even though they can travel through space and have extensive knowledge about the universe. It's simply inferior to the weapons of humans (in ground combat), even though they are considered to be oh-so primitive.
Don't repeat the same mistake and implement inferior, yet energy based weaponry! Make them reasonable and powerful.