Make a rough plan. Say, for example, I need to learn to talk about my city by September. Or, I need to be able to write a professional email by October. You need a realistic, tangible goal.
Then, make a detailed plan: I need about 150 words for this and I need to know how to talk about the past. Then I need to learn 150 more words and the future tense in order to express my views on this or that.
After that, gather some basic materials relevant to your plan. Don't just buy or download whatever looks good. It must be relevant. I suggest you make a separate folder on your computer or keep printed materials on a separate shelf in your house. If you find better materials with time, discard the old ones or put them aside for when you'll need to reasearch a detail.
Stick to your plan. Don't plan for every day, plan for checking your results once a week or once a month. However, you have to be strict. I am tired this week, I'll study double next week. Or I'll study double this week so I can travel next week.
As long as you know your destination and the 5-10 steps you need, and as long as you respect your own timetable
— reddit comment with a #language-learning-strategy
- seems very similar in core idea to ~ form language islands by drilling topic-specific sentences of your own creation