At a senior level, a digital strategist is mainly concerned with improving digital marketing and communication systems. He or she will usually manage a marketing team, identify new marketing opportunities and find ways of marketing online and through mobile networks.

As a digital strategist, you might organise a marketing or advertising campaign using ad networks, online publishers etc. A lot of the job involved liaising with groups of clients or presenting information; good communication and presentation skills are important. Usually you also need a background in media or more conventional advertising; it's very common for a digital strategist to work along with more traditional forms of media. Also, the principles of selling, reaching and growing new markets, and understanding the customer are not so different whatever media you work in.

You can get some examples of the kind of work required if you put 'digital strategist job description' in a search engine - there is quite a detailed example here.