This is a method I used in b-school and still use for CFA work.
Draw a sideways T and put + above and - below the line. Maybe something like this
Then, think graphically about what would actually happen when buying/selling puts or calls. Let’s try a couple of examples.
If you buy for $5 a call on a stock with a strike of $40, you can draw a line (from left to right) BELOW the main line (as it cost you $5, so you’re negative at the moment). Assuming the stock goes above $40, you then START to move up and to the right, getting above the $0 line at $45. This makes sense as the option cost you $5 in the first place, so you need the stock to be ABOVE $45 to make any profit.
Let’s try selling a put. In this case, we RECEIVE $5 (assuming option premium is $5) so we start out positive, so above the line. Again, we’ll stick with the $40 strike price to keep it simple. Now, we’re drawing our line from RIGHT to LEFT (as this is a PUT) and can see that we stay profitable as long as the stock is above $40. Once it gets to $40, we start losing money, and for the person that bought the put, they start becoming profitable. For example, if the stock ends at $20, then for us the end profit is +$5 (premium we took in) and -$20 (cost to buy the stock on the market for the person who exercised the put). All in, +$5 - $20 = -$15 loss.
Hope this is helpful.