My thoughts on learning languages:

The main thing to know is: learning a language takes a lot of time. Studying every day is the best strategy. If you miss a day, no worries, just do it the next day, but aim for a little and often, rather than big study sessions at long intervals.

Try to practice all skills (reading, listening, speaking, writing) evenly. Personally, speaking makes me very self-conscious and I'd rather avoid it... but it's got to be done, even if I do it very quietly or under my breath.

Do things that are fun! Listen to music in your target language, watch cartoons, try cooking a typical food from the place where your language is spoken, or watch videos about your other hobbies. You don't need to understand everything, just pick out what you can and get used to the way the language sounds.

If you want to use an app to learn, I'd suggest asking others who are learning your target language which apps they use and how it works for them.
All apps seem to have good and bad points.
Try to find one that gives you information about grammar and also cultural tips (about politeness, ect.).
I would also advise anyone to not solely rely on the app and nothing else, so that you can avoid just learning to "win" at the app like it's a game. Try a textbook, videos, podcasts, whatever you like. It's good to transfer the knowledge into another setting.

As a beginner, make a note of the simple questions you learn (e.g. "How are you?"), and use them to practice speaking and writing.

If you like to write, consider keeping a language journal. Writing about your everyday life and the things that interest you will help you build a more personal and useful vocabulary and you'll be able to look back at it and see how much you've improved.
Here are some journalling prompts/questions you can use.
If you don't like to write, you can still use the questions to practice talking to yourself or other people.
You can also search for questions in your target language on Tatoeba.

When I feel like I haven't made much progress, I remember that someone once said "Learning a language is like building a mountain with a teaspoon". It puts the size of the task back into perspective for me, and lets me see how much progress I have made.

It takes a long time, but it's worth it.