Scratch

Try to avoid too many broadcasts, infinite loops, and sounds. Those have a tendency to really slow projects down.

well making less infinite loops helped a lot theres no sound though and theres about 5 times where theres broadcastsbut there is quite a few infinite loops, about 7-10

I don't see this one often but graphic effects (color change,etc) especially in multiple on-screen sprites will add major lag quickly.

Here is another one, rotating really big sprites can also cause lag.

Often times, things may seem to generate little lag until you get many scripts and sprites running at once. A good sign is a project that is running pretty well but suddenly slows when "something" happens on the screen. Obviously, that "something" or part of that script block is causing the problem.