Contractions. Who are you addressing?
This issue and the tone you wish to give your piece are crucial to establish if you can use contractions or not. So, who are you addressing? Where is your text going to appear?
If you have to write an article for a teens magazine, contractions are OK. If the magazine is for adults, you should be more cautious and use them less.
Contractions are possible in semiformal language, but not all are justified, so if you want to be cautious, turn them all into full words.
In any case, don’t abuse, and don’t use them in the opening sentence or to initiate paragraphs.