1. Label objects around the house with sticky notes.
Even though your parents may not be pleased with little pieces of paper littering their house, this is one of the best ways to learn the names of various household objects. What better place to start than with the objects you use on a day-to-day basis? Every time you pass by or use the object, you read and say the name out loud. Once you know the word and can recall it without looking, you take the sticky note down. You can then label other items and repeat the process.
I love this app. Duolingo is free on the app store, and can also be found online here. While I use it to learn Portuguese, it offers a variety of other languages as well. The app has small lessons that teach conjugation, useful words, and even pronouns. For every lesson completed, the user earns points. These points can be used to unlock further language lessons. The app also prompts you to "practice weak skills", so you do not forget any learned material.
3. Study Preach My Gospel next to a copy in your foreign language.
I have heard from many missionaries that this works wonders. However, make sure to learn the lessons in English before attempting to learn them in another language. It is more important to know what you are teaching well before attempting to do so in another language. With that in mind, the process behind this is simple. With both books, it is easy to pick out words and sentences and translate them from English into your language. If you do not have a hard copy of Preach My Gospel in your foreign language, lds.org has all of the material online and you can translate the page into it here.
4. Babbel.com gives ten helpful hints to learning a language quickly and effectively, which can be found here.
Remember that teaching and learning the gospel are the first priority, and that you will learn how to speak your language both in the MTC and out in the field. However, becoming familiar with the language you have been called to serve in can be pretty important as well. If you have any additional tips on learning a language, feel free to comment below and share! :)