What would be the best technique to separate an insoluble solid from a liquid, like sand from water?

Filtration. Filtration is good for separating an insoluble solid from a liquid. (An insoluble substance is one that does not dissolve). Sand, for example, can be separated from a mixture of sand and water using filtration.

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

In order to improve results, many different steps can be taken into account. 1) using more precise scales and thermometers is always something that should be considered as being precise means that you are more exact with your answer.2) increasing the sample size should also be considered, if you have a bigger sample size you are able to determine if your results are accurate as well as if there are any variables that should be taken into account plus it assists in the statistical analysis and produces overall better data3) using better handwriting is also a plus, along with organizing the data properly so that others are also able to read the results and even redo the experiment in the future if it is needed.