"Time blindness" is a major symptom for people with ADHD -- difficulty telling how much time has passed, what time it is, and estimating how much time a task might take. So increasing time cues is very helpful -- a clock in every room, located on a good sight line. Use an egg timer for how long you want to spend on a task or project. Or set alarms that you have to physically get up and go turn off, rather than an alarm on your watch or computer that is too easy to dismiss or ignore.
Using a planner or white board helps get an overview of the day or week, and helps with defining priorities for the day. People with ADHD might resist writing down to-dos because they may be afraid of a resulting huge list, but writing it down is better then the anxiety that results from trying to hang on to everything in your head. Use sticky notes or the planner and assure yourself that writing it down is helping you by getting it someplace safe and out of your head!
Very importantly, be kind and patient with yourself. ADHD symptoms in our production-oriented society can feel very frustrating. Being mean to yourself doesn't help solve problems. Remember that not having a good system figured out is temporary -- don't beat yourself up for not paying bills on time, instead tell yourself, I don't have this figured out YET so I need to sit down and break it down into smaller steps. Finally, ADDitude is a terrific ADHD resource for people to know about!