Organization is needed to make your experience with Rosetta Stone a success. Determine a certain time every day or a couple of times every week where you can spend an hour or so uninterrupted on your computer with the Rosetta Stone package. The more often you practice, even if it is for less than an hour, the easier it will be to learn another language.
Especially after the first level, keep a pen and paper beside you while you are working on Rosetta Stone. Jot down the words that you don't quite understand. Additionally, when you are going through the lesson, questions may arise; write down the questions and research the answers at the conclusion of the lesson.
It is often helpful to be able to quickly look up a word or phrase in a dictionary or grammar book. This is particularly true after the first level. Additionally, understanding grammar is important. Rosetta Stone does not want you to get so bogged down in grammar that you are constantly analyzing how to speak. However, getting an understanding of how verbs work, for example, is helpful. With some languages, a verb book is also a good idea.
While you are learning according to Rosetta Stone, often you will want to learn how to say something quickly that they may not get to for many lessons. While you can look up words in your dictionary, language does not translate word for word. Often a foreign language changes the order entirely in which one expresses something or says it in a way that would seem odd to the non-native speaker. So in addition to a dictionary and grammar book, often a phrase book can be helpful.
Practice speaking whenever possible with native speakers of the language. This forces you to use the language conversationally and get comfortable with it. Ask the native speakers to correct you when you say something incorrectly.
Latin American Spanish with Rosetta Stone is a good example. The sounds of the Spanish language vary considerably from Mexico to Costa Rica to Bolivia. People from the area you are interested in may pronounce words or phrases slightly differently from how you are learning the language. Talking with native speakers will help you sound more like a native yourself.