Most of the big manufacturers offer free training on how to install and most importantly sell their gear. Lutron, Rako, AMX, Crestron and KNX are to name but a few. Some others such as Dynalite, NuVo and Control 4 either charge for training or ask you to invest a few thousand in their gear before training you.
My first piece of advice would be to do some research. Find out what you want to offer your customers as there's no point getting trained up on a system like AMX or Crestron for example if all you want to do is smart lighting, A/V and simple control as you'll price yourself completely out of the market. Then again, if you want to offer services in PA systems, conference suits, multiple source A/V distribution and high demand network integrated solutions, then Rako and Lutron aren't gonna help much. In most cases however, for the average smart home installer they will most likely have an in depth knowledge of all and more of the brands listed above and their products. The best systems these days utilise a mixture of loads of different technologies.
When I started, I started simple and progressed from there. My advice (based mainly on personal preference), after doing your research give Lutron or Rako a call first. Start with lighting and audio, then move on to wider integration.
And finally, good luck! It's a completely different industry to electrical installation. After my first day training with AMX I felt like my head was about to explode!
