Having gone to school in Sweden, I started learning English at the age of 10. Three years later, every pupil had to choose to study another second language, which in my case turned out to be German. As in most Swedish schools, there were always many language classes either in English, German or French. This lead to a good, solid knowledge of both English and German, which correlates with the usual saying that one can only learn a language really well or fluently if you start before the age of 15.
This is quite a discouraging fact for all grown-ip internationals who now try to learn Swedish, but luckily the theory behind this piece of fact is not set in stone. You can achieve very good language skills even though you start picking up a new language later in life, as an adult. Believe me, I am actually doing exactly that right now. Being in my late 30´s and trying to learn a new language, Danish, I have fully got the insight, that it is more a question about activity, contact, and frequency.
To be active and actively use new words and phrases is one of the most essential parts. Easier said than done, especially with Swedish, since Swedes insist on answering back in English as soon as they hear the slightest of a foreign accent. Personally, I find some comfort in, and help from, the digital world. Hence, I try to write shorter messages in Danish to my Danish friends by using Messenger or Whatsapp. In the beginning, I had to look up several words or ask back for the correct meaning. I also began copying my friends´ phrases for “have a nice day”, “have a nice weekend”, “good luck”, “get well” etc., and used these when replying. Out of the context, you can detect a lot of words and the meaning of several phrases although your language skills are at a beginner´s level. The short length of the messages also enables the learner to have a communication that is both fun and helpful and one does not act as an obstacle for communication. Having this said, in lack of a native speaker, I recently heard about non-Swedish people from two different linguistic backgrounds encouraging each other´s language development by using exactly this kind of communication.
Being in the country where the local language is the one you are learning, is like being in candy store for a kid with a sweet tooth. You can learn so much, just from a train ride for example. Formal signs and instructions in public transport, or in other public places are usually the same as in your language or in English. Hence, by reading these signs a few times, you will detect the meaning of words and pick these new words up. In this way, you have a closer and better contact to Swedish than you would have imagined in the first place. Step by step you pick up new words and phrases until a small part of another culture, the Swedish one, is releaved to you. This kind of experience is great but it also requires a sense of curiosity.
Being a sporty person whose second home is the gym, I often make comparisons between training and language learning. Hence, if you do something often, the result will be better and more solid than if quite some time goes by in between the sessions. Regardless if you studying on your own, only going to language cafés or attending a language course, the pace of your progress coheres a great deal with the frequency of your study sessions, your attendance at the language café or if is a semi-intensive or intensive course. In the beginning, a higher frequency is strongly recommended to really get into the language, get a good base and to tune into the new way of thinking. (In my experience grammar can be quite a new thing for many adult learners.) Hence, study every day, go to language café a couple of times a week or sign up for an intensive course.