#Preliminaries
Avoid interference from nonsensical embedded metadata (some rippers embed them too)
Settings - Server - Agents - Shows - TheTVDB
In there, grab the line ‘Local Media Assets’ with your mouse and drag it downwards, so it ends up being at the bottom of the stack of active agents.
Create a folder to hold your tv shows.
Put it outside the folders where you store movies. It must be completely separate.
Then create a new library of the type ‘TV Shows’ and point it to your newly created folder on disk.
#The crux of the biscuit
The key to tv episodes is meticulous preparation of your video files in regards to naming the episode video files themselves and organising them into suitably named subfolders.
- Look up your show on TheTVDB
- Take the title as it is used on TheTVDB. If there is something in parentheses, take that too. If the title contains invalid characters (depends on your file system), like
§ : % *, simply leave them out. - Check the naming and the folder structure of your show. Name the top folder of the show exactly after the title on TheTVDB. No abbreviations. No additional subfolders. No aliases.
- Name the episode files according to the above linked naming guide. Use the same title as for the top folder.
Show's Title - s01e01 - additional info.ext(’- additional info’ can be left out) - After you corrected the naming and folder structure, perform the Plex Dance with all files for this show.
Step 5 is only necessary if you did already add your tv episodes into Plex and they were promptly mis-identified 
Steps 2-4 can be made painless and fast by using Filebot
Make sure to not only install Filebot but to also set the {plex} naming pattern in its preferences.
There are introductory videos available for Filebot.
Adhering to the above will prevent almost all of the pains that new users report in these forums 
