and where of course not to place them
If you a begging comm you might not really think much about specifically wear your placing your buildings . in fact you may think very little at all about where you place stuff because you think other stuff is more importent. but let me tell you that base set up can be a critical part of the game.
IPs- the IPs are literally the heart of your marine team, so placing them in the right spots is importent. here are a few rules to follow when placing IPs
1- spread IPs apart so that if a solo skulk is spawn camping your marine start its easier for you to stop him.
2- avoid placing IPs really close to the armory. thats a hive traffic area for marines and often can result in telekills. instead place IPs next to buildings like the Armslab and the Observatory, where only the aliens will be going (in case their trying to attack them) that way you can maybe get some lucky tele-frag kills.
Arms and Proto Labs- the Arms and proto labs are two of the most valuable structures to marines and two of your greatest assest. thats why placing them in the right spots is importent.
1- don't put an armslab right next to your proto lab. it may be easier to check upgrades on both if there really close but instead learn your hotkeys well and keep the seperate, that way splash damage from Acid rockets and Bile Bombs can't effectivly hurt both of them at the same time.
2- smashing them into corners may seem like a good idea but is often not. if an armslab is close to a wall there my be a small spot that a skulk can wedge itself in and not be hit by deffences like turrets and can do a lot of damage to them.
TFs- turret facotries are vital to the offence and deffence of the marine team and are very importent where placed
1- do the the range Vs melee game NS is putting a TF in a long hall way or big room will allways be the most effective place. avoid jaming them in corners where sometimes skulks can get up in.
Turrets - Turrets should be used to a minimal amount, while they are effective when used properly, they are rather boring and make for long drawn out games. but still place them in good spots.
1- remember to Trianglulate your TF, to effectivly cover your TF you need 3 turrets. while it is somewhat possible with just two. it makes for a weak deffense. also while turrets in some places are a pain for aliens, they can also hassle your Marines a lot as well.. avoid clogging up hallways with tons of turrets and sieges. it really gets annoying for your troops
and thats the main jist of advice for when your placing your structures.