Pharmacology is by far my LEAST favorite part of nursing! One of my programs requirements before giving medications in the clinical setting is to obtain a 100% on our medical math (this includes dosage/calculations for drip rates and medication administration) test. Yeah not easy. BUT I have found the best way to learn it...is to do it! Practice equations over and over again. Memorize the formulas and know basic conversions ( 1L= 1,000ml, 3tsp=1Tbs, etc.) if it's specific medications you need to know buy yourself a current Nursing drug book to stay on top of the latest information of commonly prescribed drugs. Make yourself drug flash cards to study with. Remember many drugs seem similar with side effects so focus on the particulars that make that drug different then others.
Also there's an online program through ATI that tests you and shows you your strengths and weaknesses with pharmacology and how you can improve on those areas. Best of luck!