It is very easy to get low level links(by spamming) and difficult to get natural & effective back links by using white hat seo techniques.Don't keen to build backlinks quickly so Google consider spam. You have to go like slow & steady wins the race. I will not mention link strategies like forum posting,directories,articles etc. You know already but try to build natural backlinks by writing something unique.you can read anywhere over internet but write in your own words and write what do you think and feel . Write your reviews about anything which product is come in market. A original content that is to be not present over internet.write in points first then explain into 3-4 lines so reader can understand it easily. I am doing same and getting expected results.