If you are talking about marine gameplay, I would first keybind a hotkey to pick up your dropped weapon/item. Xeno gameplay involves stunlocking, so being able to immediately pick up your weapon instead of fumbling with your mouse is better.
If you are new, I would stick with one weapon with the most impact, which would be the m41a mk2. I am a full-auto believer ever since they nerfed the shit out of point blanking (pbing) xenos. You can try spriteclicking a xeno that is adjacent to you with burst-fire and then you realize half your clicks wont register as they put some stupid delay on pbing a xeno.
Luckily, it is pretty easy to make full auto viable for the m41a mk2 by either having a reflex sight or vertical grip. You can use a combination of reflex sight+angled grip for instant wielding, or magnetic harness+vertical grip for less risk of losing it. I always ask requisition for spare attachments, especially for reflex sight/magnetic harness and angled grip, as those get taken fast at squad preps.
For a short guide on full-auto, you pretty much hold down the mouse button and hover your cursor on the xeno while following it until its dead. If the xeno is right next to you, make a habit of holding down mouse button a couple tiles away then hover the cursor on the xeno (thanks for the tip @basilherb SG guide). Otherwise, if you hold down the button directly on the xeno adjacent you, you will only shoot them once.
Once you get gud, you can start carrying a secondary weapon such as the m37 shotgun with buckshot, which has insane value in being able to one shot pb runners and you can start stunlocking various t1/t2’s.