You can use Present Tense after "προσπαθώ να" if you refer to a repeated action.
Προσπαθώ να τρώω ελαφρά το βράδυ. = I try to eat light in the evenings. (να τρώω indicates an action that happens every day, a repeated action, a habbit)
You use Future form after "προσπαθώ να" if you refer to an action that happens once.
Προσπαθώ να φάω και δεν μπορώ, γιατί είμαι άρρωστος. = I try to eat but I cannot, because I am sick. (να φάω refers to an action that happens today or now, it's not repeated)