Having English as a second language, you are correct that you have to practice speaking it. It is amazing how different languages are in terms of breathing and rhythm. All I can say is try to speak it as much as possible, and especially listen to it a great deal, and try to pick up the rhythm of the language. Duolingo is great for learning the basic language, but I suggest maybe watching some Spanish tv-shows or such to get a feel for how the language is really spoken. Lots of English-speaking language students seem to make the mistake of only studying language through educational mediums. For example, I attribute my high level of English to American television, not school.