Finding some Profitable niches to blog on that are low competition can be hard since there's a lot of competition on a lot of niches out there.
To find out some keywords to rank for and create a blog around go onto Google Adwords Keyword tool and search for keywords and then build your website around those keywords that get the lower amount of searches per month if you want a chance at ranking.
Some niches that are lower competition are Dog Grooming, Tiny Houses, GPS Car Tracking, Laser Tattoo Removal, Car Shipping, Security Systems, Green Living, Party Ideas for Kids, Soundproofing, Heavy Equipment Rental, etc.
When blogging you should use Long Tail Keywords in your content and in your blog title and blog content URL.