"You have to learn more."
Translation:Du musst mehr lernen.
no. Well, a first hint, where not to put "zu" are modal verbs: wollen, müssen, sollen, können, mögen, sollen and the auxillary verb "werden" (which gives Futur I). Also verbs of movement don't have "zu": einkaufen gehen, tanzen gehen, schwimmen fahren. Besides that it is difficult to find a rule where to put "zu" and where not. Infinitives following nouns do generally have "zu": http://german.about.com/od/grammar/a/The-German-Infinitive.htm