What are some common points I can use in 15 an 25 mark questions?

Government vs market failure,  when evaluating a paragraph you can simply fall back onto stating that the action brings the risk of government or market failure ( whichever is applicable) which would result in a deadweight loss, this opens up the opportunity to add a diagram of the deadweight loss to further increase marks by demonstrating application to the examiner. Free market vs Keynesian economists,  when trying to develop a point you can base one on the viewpoint of a free market or a Keynesian economist, for example, "A Keynesian economist would argue that a tax on demerit goods is the best course of action to reduce market failure of overconsumption through raising prices". This can also be applied when trying to evaluate a point for example "A free market economist would argue that the use of a minimum wage to increase employment is the wrong course of action as it leads to increased real wage unemployment since the market wage rate is stuck above the equilibrium rate".