Let me respond from the point of view of someone who is currently (but not always) highly motivated in language learning, and who is married to a fanatical language learner (
@Wendy Werneth).
A word
@Arctic_Alex used three times in the OP is
motivation, and this is of course the key to everything. People often say about Wendy something like, 'She is so motivated to learn languages.' And she is.
But let's say you have a friend who likes watching movies. Perhaps every week they go to the cinema 1-2 times and watch several more movies at home. Would anyone say that they are 'motivated' to watch movies? No. And why not? Because in our minds, we categorise watching movies (or sports, or other such activities) as something that is inherently fun, while language learning is categorised as study, something that is not fun and therefore that requires motivation (the generally poor level of instruction in foreign languages at school is a large contributing factor in this, but that's a conversation for another day).
So the short answer is this:
make language learning fun.
I asked Wendy to reply to this thread and she declined because she essentially does not understand not being motivated in language learning. It's inherently fun for her so she doesn't need to motivate herself, just like the person who likes watching movies doesn't need to be motivated to watch a new movie.
Making language learning fun is easier said than done, of course, and even more so at a beginner level when you can't access a lot of great material. But the key to it is essentially this: do what you like doing in your native language in your target language, and then it will be fun for you.
We are understandably focused on speaking in language learning. And of course, speaking well tends to be the end goal, and for good reason. But in your own language, you do far more input than output.
And that's the second key: input (that is, listening/watching and reading). Input is how you unlock output in a foreign language -- i.e. it's how you learned your native language as a child. And, if you consume the right content for you, it can be fun simply to consume it, so that the learning happens naturally as a byproduct.
For example, I listen to history podcasts (e.g. Hardcore History, The History of Rome etc) for fun in English; therefore, it makes sense if my level is high enough that I would do the same in Italian, which is my current focus language (e.g. Storia d'Italia).
As a second example, I have always enjoyed reading fantasy-type books in English as a child and as an adult (e.g. Narnia, Tolkien's books, Harry Potter etc). So I am doing the same in Italian. In the last three months I have read 8.5 books written by the Italian adolescent fantasy author Licia Troisi. I read them in LingQ which is (among other things) essentially a tool to help you to read in a foreign language. I have read about 30 books by the Spanish adolescent fantasy author Laura Gallego in the last 12 years. Reading her most famous trilogy (Memórias de Idhún) was literally the biggest factor in allowing me to take the next step in Spanish. Reading is magic, as Wendy says.
These are just examples of the kinds of things you can do, according to your own interests. If you like music, listen to music in your target language. If you like soap operas, watch soap operas in your target language. Use tools like LingQ (and I'm sure there are others) to import books or content from YouTube or Netflix or wherever to assist with things like transcriptions/subtitles to allow for greater understanding. This content would ideally but not necessarily be aimed at native speakers, including at children for beginner learners.
The two themes I hear again and again when polyglots speak about their language learning success are to
listen/read extensively, and to do it
every day. Consuming content that you're interested in motivates you and gives you the grounding in the language that you need in order to be able to speak well.
In today's connected world, there is an enormous amount of content available to consume for major languages (including Spanish, obviously, as that's likely to be our focus here -- Notes in Spanish is one good example at multiple levels). The excuse of not being in the country where the language is spoken is, these days, just that.
I live in Portugal but with my current language focus, I am exposed to far, far more Italian than Portuguese on a daily basis, because I am choosing to surround myself with Italian through listening, reading and iTalki conversations. For example, I just watched a 25-minute video on Dante before writing this post, and when I finish this post I'm going to read the transcript of the video to enhance my understanding of what I watched and to pick up some new language along the way (listening and having access to the transcript is gold). I once took a course in English on Dante for fun, so watching this video in Italian was also fun.
In a nutshell: figure out how to consume lots of content in your target language in a way that is fun for you. That's when you reach the secret Wendy level where language learning is fun, motivation is inbuilt and when you wake up each morning you can't wait to get started on it.
I hope this helps.
P.S. Apps like duolingo have realised they can making language learning fun through gamification, but they are not actually very effective by themselves.