Newsletters—send every 4-6 weeks to your own and to external agency databases. Keep the design consistent, be concise, informative and avoid a hard sell, you want to encourage regular readership.
E-Shots—need to look attractive, offers grab attention. Work with an agency that maintains relevant databases and can advise you on implementation.
Social Media-is powerful and good for niche areas. Activity must be maintained making it time consuming.
Pay Per Click—applies to classic Google type searches and to Social Media. It is easy to spend a fortune, so work with a skilled agency, they should save you money.