The biggest thing is to know the different locations for the ini files:
\My documents\my games\xcom2\config
\Steam\steamapps\common\XCOM 2\XComGame\Config
\Steam\steamapps\workshop\content\268500\ specific mod number
Always make a backup of these folders after a fresh install so you can revert back if you mess something up. Here are some places to start:
http://www.pcgamer.com/how-to-tweak-xcom-2-ini-files-for-fun-and-danger/
https://www.reddit.com/r/Xcom/comments/47cxr2/how_to_edit_the_weapon_ini_files/
https://www.reddit.com/r/xcom2mods/comments/4c6qrr/new_way_to_loadsave_ini_configs/
Personally I love these edits:
Max Squad Size Fix mod # 619112580
First, increase the squad size: \SteamApps\common\XCOM 2\XComGame\Config\ DefaultGameData.ini - m_iMaxSoldiersOnMission Set it to 6
Second, increase the UI limit: Go to \SteamApps\common\XCOM 2\XComGame\Config\ Open up DefaultUI.ini - MaxDisplayedSlots Set to 8
Increase the Avanger pawns visible: XComGame.UIOptionsPCScreen], and change the MaxVisibleCrewConfig at each level to your desired crew size (~30).
Full Character Customization from the start \My Documents\MyGames\Xcom2\config Change VeteranSoldierRank=3 to VeteranSoldierRank=0
Add shotguns to any soldier Navigate to the class mod's mod folder. Search for AllowedWeapons.
Looks like this: +AllowedWeapons=(SlotType=eInvSlot_PrimaryWeapon, WeaponType=”rifle”)
below that line, add:
+AllowedWeapons=(SlotType=eInvSlot_PrimaryWeapon, WeaponType=”shotgun”)
Field Medic Class – 643394337 Grenadier and Gunner – 662424686 Sniper – 658531225 Infantry – 632648555 Juggernaught – 634831620 Rogue – 618036260 Trooper – 618090572
Allow a soldier to carry more than one med kit
Remove "UniqueEquipCategories=heal" under [XComGame.X2ItemTemplateManager] in \My documents\my games\xcom2\config\XComGameData.ini.
Cheers, good luck commander!