Most stories need a plot. Some are just "slice of life" recorded without defined parts, goals, climaxes, or resolutions. If you write the type that needs a plot, then that plot needs structure, purpose, and an appropriately satisfying end. There are some very definite things to avoid, too, if do not want to cheat your readers.
Plot and Subplot
Pantsing vs. Plotting
Popular Plotting Plans
The Plot River - Deep and Wide
Character Driven vs. Story Driven
What is a Subplot and Why Have Them?
Plotting a Subplot
Effective Subplot Examples
Boring Beginnings - Lack of a Hook
A Note on Series and Serials