Heuristics for creating a model

Keep it simple. Use the leanest model for the purpose at hand.

Plan your output. What will you do with it and how do you expect it to look?

Think yourself into the problem.

Be on the lookout for upper and lower bounds.

Choose appropriate spatial and temporal scales. What does the model see or not see at those scales?

Keep a list of assumptions and review them frequently. Hat the "guts" to make assumptions.

If in doubt, leave it out. Revisit the decision later.

Use salami tactics. you may not be able to solve the whole problem in one step. Slice the problem and solve it as a series of steps.

If a formula is used, be sure to understand why it fits. Be cautious of pulling formulae out of books and using them without understanding the assumptions behind them.

Cut through "Gordian Knots" by making a simplifying assumptions (but list them!).

Plan not only to test a range of parameter values (sensitivity analysis), but also to test the major assumptions you have made (assumption analysis).

Press ahead. Don't get bogged down. Get something working as soon as possible and learn from what you have done. Be prepared to throw away your model ans start again.

Be prepared to explain your model. Never put anything into your model that you cannot explain.