Consistancy is important. Do not mix tense (except between the author and the work as noted above). Choose a tense and stick with it.
Also, you don't really know what a writer intended to say...it's your opinion and should be stated as such. IMHO.
"I believe..." "I argue..." "Eliot suggests..." then evidence to prove. Every teacher or prof has different guidelines for choosing your point of view.
Hope that helps,
ps. my first post so, hi all:)
4th yr engl. major.