I have a hilariously bad habit of forgetting things.
Well, I suppose this makes me a touch scatterbrained, but I've learned to overcome this, and I shall teach you how, as well!
1. Make lists
I love lists, and I'm always heartened to know that I'm not the only one. An accounting professor of mine once declared his love for lists in-class, and even sheepishly mentioned that he loved putting things he'd already done on there, just so that he could cross them out. Made him feel accomplished, which (frankly) I can completely understand.
Lists are a great way to have a full view of everything you need to do. Once you have a list -- of the most pressing concerns, or of all your concerns -- you can prioritize and map out a course of action. As with project plans, it's important to understand the full scope of a task before embarking on it.
And, just as important, when a task is complete, mark it through and let it be. If you've done your homework and if you are as good at your job/school/work/life as you believe yourself to be, then let a completed task remain untouched for a little while. Once you have distance, you will have perspective; it behooves you to give yourself time away.
2. Color Code
In addition to lists, I love colors. I know more than a few people who color-code large wall and desk calendars by task category.
Why bother with this? Well, for one, it makes it easy to see, at a glance, what kinds of activities dominate (or will dominate) your time in the present/near future. It's also an easy way to help you manage your time; if you have a lot of personal commitments set to happen, then you know that you'll need to work out your professional commitments ahead of time.
In a similar vein, color-coding is a key way to know where things belong, and it makes a search for a specific item -- email, engagement, document, notes -- that much easier to find.
3. Be consistent
The last tip that helps me keep from forgetting things involves being consistent in my life. When I still lived on-campus, I would always hang my keys on a hook by the door, my glasses belonged on the desk or in their case on my nightstand, and I kept library books on the sill lest I rack up overdue charges. Similarly, I would tack up the to-do lists on the corkboard above my desk, and papers went into folders that matched up with their notebooks: game theory in the red folder and red notebook, whereas international economics was all blues. I don't think I lost a single paper my entire college career -- until I purged at the end of each semester, of course.
Consistency is, however, a double-edged sword. When one develops a habit of keeping Item A in Location X, placing Item A absentmindedly in, say, the fridge (how many times have I found the TV remote control in the fridge? My gosh, too many) means that when we remember that we need Item A, we scramble desperately to find it. It's why stuff is always in the last place we look. (Of course, that's also because the last place we look is where we find things; we don't need to look anymore once an item is located! #ThisIsAPun)
That said, forcing yourself to keep to deeply rutted patterns is important, as it keeps you from losing things. And that, above all, is the goal. It might make you a bit boring, being so predictable, but if it means you never lose a page of notes from a client interview, or from an expert witnesses's trial prep, or your instructions from an account-holder of your fund, then perhaps a little boring is worthwhile. After all, consider how much value would be lost if you misplaced something!