Usual mistakes.

Present and Past Tense 
   Present Simple: I Work 
   Present Continuous: I am Working 
   Present Perfect: I have worked 
   Present perfect continuous: I have been working 
Avoid the Overuse of Adverbs

incomplete comparisons
   It was much hotter today THAN YESTERDAY.
   
Misplacing your modifiers
   He almost walked for the entire day (no)
   He walked for almost the entire day !