leave an impression
I have left business cards in teacher mailboxes. I have left business cards with my sub notes when I do work. I have handed out cards after PTA meetings. I volunteer at after school events, such as the Book Fair, Fall Fest, Story Night, etc. I volunteer many days that I don't have a sub job. If the volunteer coordinator at your school (home and school advisor at our school), doesn't have anything for you to do, ask if you are allowed to visit teachers on their planning periods. If so, pop in and introduce yourself. Let the teachers know you are a volunteer and ask if there is anything you can do for them. That may be copywork, helping with tasks in the classroom, working with students, etc. If the teacher doesn't know you, work it in that you are a sub, but since you don't have a job for the day, you thought you'd do some volunteer work. You don't want to eat up their planning period, so be brief. If they use you, there will be time for talking later.
You really want to get the teachers to request you so you won't be as dependent on the system to get you a job. If the teacher sees you in the building a lot, that teacher may just give you a try. At the least, that teacher may ask others about you. If you wish to sub at your child's school, it helps to be an involved parent.
Personally, I work at a small school approximately 3-5 days per week. There are slow times and I could probably work more during those times, but I am not willing to work at other schools. Last week, I only subbed 1 1/2 days because it was a testing week and teachers weren't allowed to plan absences. This week, the flu is evident, so I worked every day so far. I have Thurs. and Fri. pre-scheduled, so if God is willing, I will work.