For myself, the keys have been to find the motivation and to find the right resources (at the right time).
At first I would just try to learn one new thing from The Finnish Teacher every time I studied, and I used Memrise a lot for vocabulary. Then slowly I starting using ClozeMaster too. Eventually I also could listen to Selkouutiset. And then slowly I started being able to watch videos from Finnished. Textbooks can also help a lot (like Suomen Mestari or Finnish for Foreigners 1), but of course studying from the one textbook becomes a bit boring. Finally in terms of resources: you can always try to find helpful Finns on italki or other similar platforms. At least for me, it was definitely a big mental barrier starting to talk to people I didn’t already know in Finnish, but sometimes the things that are most challenging generate the best results. Then in terms of motivation - perhaps it is something that varies a lot from individual to individual. For me watching youtube videos where foreigners speak Finnish is always really motivating, just to remind oneself it is possible to learn Finnish as a foreigner.
Websites
Language exchanges
italki
Hellotalk (app for phone)
Vocab and Memorisation
Memrise
Mondly (app for phone)
Clozemaster
Online resources
Listening
Selkouutiset by Yle
Okay so the new may not be that interesting, but I listen to this every day for months and completely credit it my current level in Finnish. I listened first without the subtitles, then wrote down all the words I understood and then listened again with the subtitles to get the words I didn't already know.
Finnished on Youtube
Interesting videos spoken by a native Finn. She also explains the methodology behind learning a new language from listening alone!
Kielikoulu by Yle
Super helpful new app/desktop application. Great for vocabularly building.
Elämä on mukavaa on Youtube
This show is so lame and ridiculous, but at least they speak fairly slowly.
Grammar
A wonderful website. You won't find Finnish grammar explained more succinctly and clearly anywhere.
Very comprehensive website, that comes grammar and vocab.
New post regularly, great for new learners.
Online dictionaries
My go to online dictionary. I also use the
version completely in Finnish.
Get some motivation for your studies...
Textbooks
Suomen Mestari 1-4
Completely used in Finnish classes. This book is completely in Finnish.
Finnish for Foreigners (by Maija-Hellikki Aaltio)
Explanation in English.
The Finnish Tutor (by Dr Riitta-Liisa Valijarvi)
This book ranges from A2-B2 level and has a lot of exercises and answers. Grammar explanations are in English.
Tarkista Tästä (by Hannele Jönsson-Korhola and Leila White)
This book has a collection of Finnish verbs and their rections. Surprising helpful for the somewhat advanced learner.
Suurella sydämellä ihan sikana
This is a collection of common sayings and idioms in Finnish. Suitable for the advanced learner.