How to get into theatre reviewing

As is increasingly the norm with many professions, most critics will be working for low or no pay at the start of their career. One caveat to this unfortunate trend is with that modern technology means that anyone with the desire can get into theatre reviewing.
Like many of the arts this convenience means the most important thing is to establish a portfolio. This does not necessarily have to be published work, keeping a blog is a good example, the important thing is to build up a body of work.
Start your reviewing with your passion, the thing that makes you want to get into theatre reviewing, the passion in your writing should make for good reading. From there, go on and review as much as possible with plenty of diversity to show your skill as a critic.
Obviously to begin with this could prove to be expensive, but less established, or student, theatre companies will often have complimentary tickets to provide. This can be a mutually beneficial arrangement, they get critical buzz and the possibility of a good poster quote, and you get the chance to establish yourself as a critic. Additionally contacting the press offices of various venues should be able to secure you some amount of free tickets as a reviewer.
As well as the obvious financial benefits, this also allows you to build links with venues. Finally, once you have a portfolio of work, you can start to contact publications that you might want to work with. This may be as a staff reviewer or as a freelancer. Some media outlets advertise but the best option is generally to approach them with an example of your work.
Gaining momentum and making inroads is the hardest part but it is a very rewarding job, so preserve and reap the rewards.