First, make a list of all your prescription drugs, dosages / monthly quantity, and annual costs (you may wish to ask for help from your physician, nurse, or pharmacist).
Are your prescription drugs on the plan's formulary (prescription drug list)? -- (please note: listing out your medications and checking them against the formulary is probably the most difficult task.)
If you are looking for a prescription drug plan with a copayment feature (paying a fixed cost for a certain class or tier of medication), you may want to record the cost of the tier and where your medications are classified. For instance, if you are using LIPITOR (r) and it is a "Preferred Brand-Name" drug, take note that co-payment for Preferred Brand-Names is $30 (or whatever the plan stipulates).
List the costs with each medication to determine a monthly cost figure.
If your prescription drugs are not on the formulary, are there alternative prescription drugs listed on the formulary that your physician can recommend?
If you need new prescriptions, do you prefer name-brand or generic prescription drugs?
Are you looking for a plan with a Mail-Order option? or an option to purchase 90 days at one time?