There is a lot of evidence which suggests that it is better to learn a second language when you are still young, ideally before the age of 11, and that once you are a teenager it is more difficult to learn a foreign language. This might be true but there are plenty of examples of adults who have started to learn a second language later in life and still managed to achieve a very good level. There are lots of factors involved in how well people are able to learn and use a second (or third or fourth) language and age is only one of them.
Here are some tips which might help you: Firstly you are likely to learn a language more quickly the more exposure you have to it. It, therefore, makes sense to try to spend time in a country where the language is spoken. You do not necessarily have to go and live in the country long term but try to make frequent visits so that you often have to use the language for genuine communication and see and hear the language all around you. It is important that even if your visits are short they are frequent so that you do not forget everything you have learnt in between one trip and the next.
If you go with friends who speak your language it is unlikely you will have much need to use the language you are trying to learn. Probably the best thing to do is to go alone and enrol on a language course so that you will have some instruction and help with the language from a teacher and you will also meet other people in a similar situation to yourself. Of course, this might not be possible, it might be too far away or too expensive. Don’t worry, even if you stay in your own country and learn another language there are still things you can do to make the experience more effective. It is possible to try to teach yourself; you can buy some books, borrow material from a library or follow an online course but the best thing to do is sign up to have language classes with a qualified teacher. It is more fun to attend classes with other people and you can often help each other and learn things from other students so you are likely to make more rapid progress than if you try to study on your own.
In addition, you want a teacher who will give you homework and correct it for you and guide you in what other things you can be doing outside of class by yourself. One thing you should definitely try to do is read in the language you are studying as reading is the best way to increase your vocabulary.
When you are reading you will probably come across language you are already familiar with in new and different contexts. This helps to broaden your knowledge. For example, you might see verbs you already know in different forms. It doesn’t matter what you read, and the best advice is to read something that you would read in your own language. Reading in a foreign language can be difficult, so it is important that you choose something you are interested in and would enjoy in your own language. You can even read a book you have already read in your own language. When you come across new words or expressions try to guess their meaning rather than looking them up in a dictionary. It is not usually necessary to understand every single word.
That way you won’t interrupt the flow of your reading. When you come to recording new words or expressions either in class or from reading it is really important to write whole sentences and use meaningful examples.
A big problem when you try to use the language you are learning is inaccurate translation. You shouldn’t try to construct sentences and phrases the same way you do in your first language as this often results in something that sounds strange or even something that makes no sense at all. The best way to avoid this is to learn whole expressions and sentences and not to focus too much on individual words.