Events

RunService.RenderStepped runs every frame.

local connection;
connection = game:GetService('RunService').RenderStepped:Connect(function(dt)
    if (bad) then connection:Disconnect() end;
end);

RunService.Heartbeat runs every frame after the physics simulation completes.

local connection;
connection = game:GetService('RunService').Heartbeat:Connect(function(dt)
    if (bad) then connection:Disconnect() end;
end);

RunService.Stepped runs every frame prior to the physics simulation.

local connection;
connection = game:GetService('RunService').Stepped:Connect(function(dt)
    if (bad) then connection:Disconnect() end;
end);

Loops

An iterator loop runs for every incremention of x to y via incrementor z.

for i = 0, 1, 0.5 do
    ...
end

A while loop runs until the given condition is truthy.

while ... do

end

A function loop is bad:

function isbad() 
    this() 
end 
function this() 
    isbad(); 
end

function this_is_bad() 
    this_is_bad(); 
end

A repeat loop runs until the given condition provided after the until keyword is truthy.

repeat

until not bad;

Warning and Trivia

Make sure you provide a yielding function for your non-event loops. They will crash your game.

In the script builder community, which is typically centered around CFrame animation, they use a for loop. This is because CFrame:Lerp, the Linear, intERPolation function requires an alpha that signifies the progress between CFrameA and CFrameB, which can easily be given through for i = 0, 1, 0.1 do as i would be the given progress.

wait() runs according to the built-in 30hz roblox scheduler. Recommended not to use for quick action.