What should I make to practice?

I am assuming this is what you mean... If not I am sorry 2 Basic things you will HAVE to know is A) functions B) Hierarchy------------------------------------------------------------- Functions

function doMyMathHomework()
homework = 4 + 4
print(homework)
end

doMyMathHomework()

Hierarchy

MyName = script.Parent.Parent.Name
print(MyName)
print(script.Parent.Parent.Parent.Name)

Being able to combine your knowledge

function CheckParent()
print(script.Parent)
end

wait(5)
CheckParent()

when you have the basic knowledge (roblox wiki can help) then you have to figure out what you want to make! FPS, horror, adventure, etc. ------ Say I want to make a Sword Fighting game... I would make a tool, add in a script similar to this

function onTouched(hit)

if hit.Parent.Humanoid then -- should check if humanoid exist
hit.Parent.Humanoid.Health = hit.Parent.Humanoid.Health - 1 -- the value that is being taken from Health
end

script.Parent.Touched:connect(onTouched)

you would want to make a map (not hard, just unions, blocks and stuff) and then you would most likely want GUI's... but GUI's are to hard for me to explain to someone-- Sorry-- Hope this helps you a little bit!

Here's a reasonable succession of topics in Lua

If you want to practice writing something, I would look at ProjectEuler.net and see if you can solve some of the easy problems there.