[Slakah]

Where do i put the if (not my_var) then my_var = "default Val" end

In your function which is fired on "ADDON_LOADED" or "VARIABLES_LOADED".

The code I generally use for saved variables goes as follows (although I have started mucking about with metatables):

local addon = CreateFrame("Frame")
addon:RegisterEvent("ADDON_LOADED") --I use "ADDON_LOADED" because the majority of my mods use "AddonLoader".

local function OnEnable(self, event, addon)
	if addon ~= "my addon name" then return end
	
	if not AddonDB then
		AddonDB = {<defaults here>}
	end
	self:UnregisterEvent("ADDON_LOADED")

	<Register any events you want to register here>
	self:SetScript("OnEvent", MyEventHandler)
end

addon:SetScript("OnEvent", OnEnable)

Hope this helps you.