
Prioritizing demands that you assign an importance (at least a relative importance) to the tasks. If the thing you need to do are not important to you (or at least important to someone else who has the power to make them important to you, like your boss) then it's hard to put them in order of priority.
You will have many tasks to do, and they will usually fall into the "important" and the "urgent" categories. To avoid making decisions, we often categorize according to urgency (whoever is yelling at us the loudest takes precedence) rather than importance. However, we should be doing what's important first. If everyone did that, there would be few things that would ever make it to urgent because we would have prepared ahead of time. (Well, in theory... I KNOW we have ADD!)
Now, how do you decide what's important? Without goals, it's impossible to define anything as important. Once you decide what you want to accomplish (in life, or just today) you can identify the things you need to do to bring you closer to that goal. Those things then become tasks that are of higher priority than other tasks that don't bring you closer to your goals.
I don't mean to say that this is easy. It's not. It's simple, but incredibly difficult, even for people without ADD. I do wish there was a simple answer to give you, but prioritization according to anything other than the goals you want to achieve (which are defined by the vision of your life as you want it to be) becomes just an arbitrary order in your list of things to do. You could put things in a list and then put them in alphabetical order and achieve the same thing.
My daughter (who has ADHD) has no problem with prioritizing. She wants to either watch TV, play video games or talk on the phone to her friends. She has no career or life ambitions (yet) and so does not have any problems with prioritizing. She watches TV until she's bored. Then she plays games until she's bored. She continues this cycle until the phone rings. No problem! 
You can look into time management system and so on to help you, but the good ones will all come back to, "What do you want to achieve in your life?" and then guide you from there. I doubt that's what you were looking for as an answer, but I have ADD... I'm a bottom line kind of guy, and that's the bottom line. 
I am the same as you, even with my meds I have a hard time prioritizing, especially tasks that are boring to me (like housework, running errands etc) 
What I do though is each morning, after I have taken my meds is take 15 minutes for myself to write my list of what I want to get done that day and then when I am done, write down numbers by each task by order of importance (ie paying bills on time is important so that would be a #1 priority etc etc). I also "treat" myself. My big thing is writing and being on the computer, both of which let me to "dump my thoughts" so to speak. But I don't allow myself computer time until I have done at least 2 high priority tasks - so I kind of trick myself I guess and that is what works best for me.
I am a huge list maker, but then I start making lists to organize my lists
I Also carry around a little hand held voice recorder so if something pops into my head and I can't write it down I can just record it immediately and not lose that thought.
Meds certainly help, but we also have to take responsibility as well for the behavioural-cognitive aspect and work with the meds at the same time.

[QUOTE=Coldsun]I use a PDA. With the calendar function, I can put in things I have to do or apts... I can then give myself a warning at X mins or hours or days away so i don't forget. Then I also have a program that keeps track of my tasks. [/QUOTE]
Yeah, I got one of them too!
Boy, I wish I could remember where I put it 
I'm on 20mg adderall..and today feeling sad..confused.tomorrow going up to 25mg
Like I dont feel comfortable in my own skin.I have today off...and nothing is making me feel better.
Am I just having a bad day or is this part of being an adhd'er?
Have you ever thought about working with an ADD Coach?Sorry you are not feeling well today. Maybe the change in meds for tomorrow will help.whoops..I didnt mean to post in this thread, I thought I was starting a new one.
Ive dont the flylady thing..very useful..but I dont need that kind of help..i think its mostly meds and the barometric pressure messing with me.
thanks tho for your advice!