Preload enhancers: fluid! Preload = stretch, so think volume.
Preload reducers: nitrates (both preload and afterload, but more so venous than arteriole), diuretics.
Afterload enhancers: vasoconstrictors.
Afterload reducers: vasodilators. Many have mixed venous/arteriole action. Hydralazine is an example of a highly-selective arteriole vasodilator.
It's important to know about preload, afterload & contractility and how they relate to your patient. For example, for an RV infarct, you do NOT want to give preload reducers because these patients are preload dependent. If you lessen the "stretch" (volume) that can lead to decreased left ventricular filling = decreased CO.
If you have a patient with a low BP, are they volume depleted? You don't want to "squeeze a dry tank"