Initially sit in as many appointments between clients and different social workers/case managers in your agency as possible. Each case manager and dynamic may teach you something.
Connect with the client's providers to learn more about the client, coordinate his service plan, and find out what services and (this one's sometimes my favorite) goods he's getting from another agency. Particularly relevant for clients who you'll work with more intensively or clients who ask for a lot of assistance.
Get into the habit of staying organized early. As organized as possible. File papers right away. Trust me.
If you must have post it notes or handwritten notes for a short time, and these should be sparse, date them. Date them all. It may be helpful to have a notebook to keep info in one place.
If you're not able to help a client with an item (like a dresser) always give another option. Like offering to budget with her to save money to get one or refer her to a resource that may help.
Make sure you're able to read the doctor's handwriting (on prescription) before you leave her office.