Email marketing is an entire profession, and can be tough to do in-house without overworking your marketers. Outsourcing to digital marketing agencies might be the most cost-effective option for many businesses.
That said, everyone's different, and smaller businesses in particular will likely find it more cost effective to spend a little time learning the fundamentals of email marketing in order to do the job themselves. Here's your first tip: use a lot of bad puns. People love them – don't ask me why.