Copy a few articles into text files and get working on implementing some of these methods until you have enough of an understanding to construct your own methods for the fun of it.
Here's some good reading material:
https://www.facebook.com/notes/facebook-engineering/under-th...
https://www.researchgate.net/profile/Stuart_Rose/publication...
http://cdn.intechopen.com/pdfs/5338.pdf
https://arxiv.org/pdf/1603.03827v1.pdf
https://www.quora.com/Sentiment-Analysis-What-are-the-good-w...
http://hrcak.srce.hr/file/207669
http://nlp.stanford.edu/fsnlp/promo/colloc.pdf
https://arxiv.org/ftp/cs/papers/0410/0410062.pdf
http://delivery.acm.org/10.1145/1120000/1119383/p216-hulth.p...
Edit: Don't get deterred by the math formulas in these papers. They look far more complicated than they actually are.