1. Read the problem statement carefully. 
2. Make sure you understand what the problem is asking.
3. Do you have enough information to solve the problem?
4. If information is not available, see if you can generate it.
5. You may not need additional information if you change your set of assumptions, provided your assumptions are reasonable.

ENE801 Related

1. Read the problem statement to see if spatial variations are involved (e.g., concentrations at different points along a river). If so, you are dealing with distributed systems. This simply means that we cannot solve this problem using theory developed for well-mixed systems. Read the problem to see if one of the analytical solutions in the text can be used. 
2. Learn to recognize similarities in the governing mathematical equations in different contexts and learn to apply the solutions. 
3. If the problem involves a lake, a river or an estuary but no reference is made to concentrations at different spatial locations in the lake, then you are dealing with a well-mixed system (the entire lake or river is characterized by a single value of concentration at any given time). The solutions for such systems depend on what type of feedback there is in the system. For example, is the system a feed-forward or a feedback system? Is it time-dependent?
4. For a well-mixed system, always try to see if there is feedback. Write your equations accordingly.
5. Always remember the conservation equation:
   
   Keep an eye on the + and – signs when you apply the above equation. Also remember that the volume V goes inside the derivative if the it changes with time.
6. Remember that analytical solutions are derived for a particular set of boundary conditions and initial conditions. If your problem has different boundary and initial condition(s) then the analytical solution cannot be applied. 
7. Remember that a complex non-linear equation can be solved by trial and error. For example, if you have an analytical solution for the concentration in a river as a function of time, and you know the concentration, you can calculate the time it takes to reach that concentration by trial and error. A sophisticated non-linear root finding algorithm is not required.
8. You can solve inequalities in much the same way as you would solve an equation.
9. Finally, learn to make intelligent guesses.