Use of waitforchild

Should I always use it at the start of a script?
Should I use it again and again in one line?

Parent:WaitForChild(child):WaitForChild(child2)

or will this cause an unnecessary amount of yielding?

:WaitForChild()
Should be used on client scripts and in scripts that rely on other scripts to create instances.

If it’s a local script always use WaitForChild()

That shouldn’t be an issue. Once the instance is found it will continue on the script or cause an infinite yield if it never loads