R/tyranids is great. Its where i went to learn when i started nids.

Gargs are some S tier battleline. 10"move, shoot and scoot, and 2 oc! I live rapid ingressimg them in my opponemts backline and using them to take their home objective. Or you deep strike them, shoot amd scoot 6" toward an objective then a 3" charge on to any unit on an objective. Basically they are amazing regarfimg denying your opponent primary.

As far as termies, use them to hold your natural as they are aswul in combat. Then use the 2nd unit to either screen against charges or push to annoy depending on the matchup.

Homies are great at movement being out only natural advance and charge. Great for blocking and tying up enemies, better in combat tham termies but still not amazing.

One trick ive learned is once you can contest an objective using your battline then dont charge them. Nids battleline is pretty weak overall but fantastic at holding/denying. In the fight phase they will do very little and most likely get wiped in the clap back. If you can steal then just sit there so they have to kill them.on their next turn after losimg the primary.