Hashtag strategies for marketing:
Brand - campaign specific - company name or tagline - signature tag
Trending
Content
Keep the hashtag short and easy to spell as many are used on mobile devices with smaller keypads.
Do not span trending hashtags. This could get your Twitter account suspended.
Use hashtag analytical tools to help you find hashtags.
Hashtagify.me - find and analyze Instagram and Twitter hashtags
Keyhole - Real-time hashtag tracker for Twitter, Instagram and Facebook with its visual dashboard
Tagboard - web page of social search & display platform