Many districts use the standard teaching application, and collect their applications via PAEducator.net, so that's a good place to establish yourself for quick response to open positions. Other districts are one-off, so you'll have a bit of legwork in order to keep up.

Because of the relatively strong unions in most public schools here, there's not a ton of churn in the teacher base, despite the national news about teacher shortages. That said, my experience is based on my spouse seeking music teaching jobs in the area, which is pretty cutthroat given the size of most districts' music programs and the attractiveness of the career here in Western PA. You may have more luck with elementary as more and more boomers retire. Also, mid year can be a good time because there isn't a glut of new grads from all the teaching schools around here, and many established teachers did their re-shuffling over the summer. You could catch a long-term sub and/or mid year replacement position.

Also, despite the strength of the unions, most contracts don't have provisions to take new teachers' experience into account when placing you in the new job's pay scale, so you will *likely* start at step 1. My spouse just started at a new district in May and her 18 years of experience helped her get the job, but she's at step 1 on the scale again. It was a relatively big cut and will probably take about 10 years to get back to what she was making, but ultimately she decided the district/position were worth it over her previous spot.

Good luck in your search!