What do the four rules of the scientific method mean?

Answer 1

Galileo Galilei had combined quantitative experimentation and mathematical analysis, to permit the enunciation of general physical laws. Isaac Newton systematized these rules in the Principia, which became a model that other sciences sought to emulate. His four "rules of reasoning" are:

1. We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.
2. Therefore to the same natural effects we must, as far as possible, assign the same causes.
3. The qualities of bodies, which admit neither intension nor remission of degrees, and which are found to belong to all bodies within the reach of our experiments, are to be esteemed the universal qualities of all bodies whatsoever.
4. In experimental philosophy we are to look upon propositions collected by general induction from phænomena as accurately or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phænomena occur, by which they may either be made more accurate, or liable to exceptions.

But Newton also left an admonition about a theory of everything:

"To explain all nature is too difficult a task for any one man or even for any one age. 'Tis much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things."

Answer 2

See wikipedia article, especially the box with :-

The essential elements of a scientific method are iterations, recursions, interleavings, and orderings of the following:

Characterizations (Quantifications, observations, and measurements)
Hypotheses (theoretical, hypothetical explanations of observations and measurements)
Predictions (reasoning including logical deduction from hypothesis and theory)
Experiments (tests of all of the above)