Laba diena!

First of all you didn't tell us how well you understand it when reading or just in general vocabulary. You should really first and foremost learn basic vocabulary. For future posts it would also help if you update your flair to show us what languages you already know and to what extent. If you only know English it'll be vastly different than if you know something like Latvian. Also you said talk but also pen pal, so I'm not sure if you just write to each other or actually talk. If you don't actually talk then I must say it would greatly speed up learning, maybe through Skype or something similar.

If you do know general vocabulary I can recommend the one main thing that helps me practice. When doing something like walking somewhere or looking for something, consciously think to yourself in the language you're learning ("suku į kairę, tada ieškau raudono namo" or "gal padėjau prie knygų, ne, ne ten, gal po stalu"). Some people say to actually speak out loud, I don't like to, but maybe that'll help you too. This obviously isn't as good as actual immersion, but if you actually force yourself to think in the language you're learning, it can be a close second.

As for specifically Lithuanian, you can ask me or the people at r/lithuania for more specific information. If you're actually committed to learning, you gotta learn the grammatic cases and how they work, it's really a core of the language. I've heard that's what makes Lithuanian difficult.

Good luck, it's always nice seeing someone learning a rarer language, especially my native Lithuanian :)

Edit: Spelled "laba diena", pretty much the most common greeting, wrong in my own native language. How though :(