How should i start buying?

I want to start buying bitcoin, should i start buying like with 20 dollars every week or make a "big start" and at first buy with like 200-400 dollars and then continue with the 20 dollaars a week system?

Does it affect the results if i put in 20 dollars a week VS 80 $ every month when my paycheck comes in? I think it would be easier for me to invest more at once than a little at a time.