Loans are useful but can be crippling. When taking out a loan, consider whether the additional profits that you will make from what you are going to build will pay the interest. It can be worth taking the loan even if it does not if it gets you to a longer term goal - and in scenarios where you only have to make a small quantity of a cure to win, taking all available loans to get you to that goal works as long as you will win before the money burns away and you are paralyzed with debt. Try to repay existing loans when taking a new one.
The basic drugs very often require an Ioniser or a Agglomerator to increase to the next level cure so these are often good machines to start researching early. Since the concentration of the second (or third) level cure is unlikely to be similar, allow space to alter this after it becomes possible to promote the cure. It is often best to put the pill press/creamer etc near to the port and run a belt to it since this gives the most flexibility.
When planning layouts, remember that you may need a dissolver or an evaporator to improve the drug and so allowing space for this is helpful.
If there is demand for it and it is showing a profit, there is no reason not to build multiple lines producing the same drug.
When redesigning a line, it is cheaper to keep old machines and reused them than selling them and repurchasing them. This may seem obvious but it makes a big difference. Imagine that a machine costs $2200. You sell it for $1100. You buy a new one later. You have spent $3300, 50% more than you needed.
If a drug is making a loss, stop the input port or delete the belt from it. If you decide to change the initial ingredient, try to do it in a way that allows you to sell as much as possible of the already purchased ingredients. While you are making a loss on each one, it is a smaller loss than throwing away partially completed drugs.