I thing you are a SEO expert and you don't know how to improve your back link..then how can you give better SEO service to your client.
Tend to agree with slymarketing here - quality, useful, unique, content will see your website or blog gain natural backlinks....
Do some viral marketing. Write some fictional articles which you submit to social media sites like digg or reddit. The problem with this those is that you cant really control the anchor text.
back links is all about links, get links to quality related sites, do directory submission, article, bookmarking, comment etc... there are lots of ways to get back links you just need to be creative and resourceful.
write good content - spread it well over the net - using articles and blog commenting and all - spend some money for directory submissions - thats it