Use the Internet and find a good acting class near your home. Make a list of the three to five of the best schools closest to your residence and call each asking if you can observe class for free. This is imperative as you want to find a school which uses a technique that best fits your personality and has teachers that you are compatible with. Always make sure you are able to watch class before you pay any money.
Get good headshots. At your acting school ask your teacher or fellow classmates if they can recommend a good headshot photographer. Go to each photographer's website and evaluate how well that person shoots people of your age and gender. Remember the best photographer isn't the most expensive.
Find the online casting websites for your city or the closest big city to you and register, upload your photos and submit yourself for auditions. Submit yourself for everything: short films, student films, thesis films. Don't worry about getting paid; right now you just want to build a solid reel of your work.
Add each job you book to your resume along with your training and staple to the back of your headshots for auditions.
In this age of technology, however, having a reel, especially if you seek work in films, is imperative. A good reel showcases your ability to act and can often help open doors. Casting directors often call in actors with strong reels for auditions and overlook actors who don't have reels.
Post your reel online. Many actors have their own websites which display numerous headshots and their reel. While this is a useful tool, it isn't necessary. You can post your reel to your MySpace or Facebook page. The important thing is to make it instantaneously available to anyone interested in seeing your work.
Assemble a packet of your headshots and reels and mail to agents near you. Local agencies can be found by typing in the words "agents" and "the name of your city" into any search engine. Agents can get you better auditions than the ones that are posted online which are available to everyone. A good agent can guide your career and importantly, pitch you to casting directors.
Consider joining the Screen Actors Guild (SAG). People act in nonunion films for years before joining SAG, so don't be in a rush to do so. SAG is a union which protects the rights of actors, makes them eligible for health insurance and makes sure they get paid union rates and overtime. SAG is exclusive and hard to join and prevents your from taking non-union work once you've joined.
However, all professional actors eventually join SAG. There are three ways: Book a SAG commercial or theatrical job as a principal or main performer. This can be a bit difficult because as a non-union actor it can be hard to even get auditions for SAG jobs, but it is possible.
Do extra work. If you work as a background performer in a SAG film for three consecutive days you are eligible to join SAG. This can also be tricky because while working on set as an extra you need to collect a "SAG voucher" each day that you are there. Production teams can sometimes be fickle about giving them out to all the background performers and they are not automatically available, many conditions apply.
Join an affiliated union like AFTRA, ACTRA or AEA for one year and you are automatically eligible for SAG. Joining these unions have many conditions as well.