We all had contact with learning a new language, either at school or on our own initiative. I am a Polish-Russian-English (soon Finnish) translator, so linguistics is inseparable part of my life. I lived abroad and grew up in a foreign country - Uzbekistan. I simply had no choice, but to learn Russian and English in order to be able to communicate with new friends and teachers. But what if you live in your own country and decide to learn a new language? I have some tips taken from personal experience (Finnish language).
First and most importantly, you need to like the language. The way it sounds, rhythm, stress, mentality of it. It is good to begin with a grammar book in order to get to know the basics (treat it as a foundation). But it cannot be your only source of knowledge and definitely not a main one.
Second of all, find yourself a native speaker. If it is a commonly spoken language, you can find one in your city, if it is less popular, you can have some conversations on skype. It is very important to practice what you have learnt so far.
Note: Don't be afraid to make mistakes. This is the way we all learn. Speak, speak, speak and don't give up on it.
Third of all, I would suggest to buy yourself a book (it can be meant for kids or any kind that you are interested in). I would not suggest philosophy in the beginning, but for example a novel (I chose Bridget Jones). Take a pen, a dictionary and start translating it. This is the way you can learn some slang, spoken language, collocations and putting the words together (It is very important to learn the words in collocations or in sentences, combining them. It helps your brain remember). You also need to listen to the language, so if you are into movies, get on Netflix and watch them with subtitles. Stop anytime you need to hear something again . Let it be a lesson and a relaxation at the same time.
Another way is music. Find some bands that play your favorite genre and sing in the language you are studying and learn the lyrics by heart. Rhythm and sometimes rhymes will help you.
My number four tip is to buy a little notebook, which you can carry along all the time and write down words that caught your ear or ones that came up to your mind, in your language. When you are back home, use few minutes of your time and translate them. You can also download a phone translator, which is a handy way to translate things when you are on the run. Your vocabulary will be expanding every day, without a big effort.
Positive attitude is really important. Believe me, it is possible to speak a new language already after a month of studying. It is an adventure, where you will meet obstacles, but treat them as a great opportunity to learn.
Good luck!