Here is how I'd suggest you learn SEM:

#1 - Open a Google Adwords Account (You can search for free credit / promo codes) online and play around with it.

#2 - Review all of Google's training material: https://support.google.com/adwords/?hl=en&page=examstudy.cs#topic=3119071

#3 - When you finish Google's training materials, then read about Adwords on the web. Here is one good resource and you can Google for more:

http://www.wordstream.com/adwords-for-dummies

#4 - Sign up for an affiliate network (e.g. Commission Junction or Linkshare) and use your free credit to promote another company's offer.

#5 - Once you feel comfortable with Adwords, consider building out your own Lead Gen websites or selling leads to existing affiliate networks (e.g. Motive Interactive or Integrate.com)

#6 - If you'd like to learn from someone else, find an entry-level job at an agency: http://www.indeed.com/q-PPC-entry-level-jobs.html

#7 - Another good way to get good at PPC if you work in an in-house marketing role is to hire someone to audit or manage your own account for a period of time so you can learn how they think and what they do.

#8 - One word of caution: Google takes a minute to learn and a lifetime to master. Their default settings make it very easy to waste a lot of money so really make sure you know what you are doing before you spend too much money.

Read some industry blogs like semoz.com or searchengineland.com. Then, I would say try to get your own site built up and generating leads. One step at a time.

Work for a small SEM agency or at a company with experienced marketers to learn the basics. Or, start by advertising other people's products as an affiliate.

There are some great suggestions here if you want to learn things on your own. But if you want to just focus on client acquisition or want to keep it lean/simple initially - just find a good partner/reseller who provides SEM services. It's better to spend money paying for SEM services if that's not your core strength and play with your strengths in other parts of business.