How this translate to English is both the same. They are both future tense. For simplicity, an I only know simplicity, the structure is different for the same exact statement/thought. What goes after the verb will show you the difference. [Maglilinis ako. // Lilinisin ko.] [Maglilinis sila. // Lilinisin nila.] In this example for the 'Mag' version, the speaker is not aware what the doer of the action will be cleaning. In the other, there is already a definite idea what is being cleaned. [Maglilinis ako ng banyo.// Lilinisin ko ang banyo.] [Maglilinis sila ng banyo.// Lilinisin nila ang banyo.] In this example, you'd see that the version works for specific pronouns and linking words. Ako and sila, and Ko and nila, and the linking words Ang and Ng. Using the wrong pronouns or linking words will either distort what you mean, or just plainly wrong grammar. As native speaker, again for simplicity, the thought that it expresses is the same.

Reiterating what Jose wrote, to say "Maglilinis ako ng banyo." is like saying "I am going to clean the bathroom" with the intention of emphasizing to the listener what you're going to be DOING. "Lilinisin ko ang banyo." is like saying "I am going to clean the bathroom" with the intention of emphasizing to the listener WHAT you're going to be cleaning. In English, when asked either of the questions "what are you going to do?" or "what are are you going to clean", we can answer with "I am going to clean the bathroom." But in Tagalog, the first question is usually answered with "maglilinis..." and the second question is usually answered with "lilinisin..."

Maglilinis = To clean (future) Ex. Maglilinis ako ng banyo | I will clean the bathroom. *Emphasis on the doer of the verb. (I | Ako) Lilinisin = To clean (future) Ex. Lilinisin ko ang banyo | The bathroom is what I will clean. *Emphasis on the object of the verb (bathroom | banyo)