I've been struggling with this for years. Understanding through listening the most difficult because (a) native speakers speak very quickly and (b) it's completely out of our control. The other three aspects (reading, writing, speaking) are all guided by ourselves in some way, shape, or form, but not listening.
One strategy I've found to be helpful is to read out loud. By reading out loud, we're training three of the four aspects of language-learning (reading, speaking, and listening), whereas reading in silence only trains one aspect.
I recommend listening to lots of Spanish audio in order to 1. familiarise yourself with the sounds and speed of the language 2. begin to pick up new vocabulary (as long as you actively listen rather than just having it play in the background) 3. internalise sentence structures (in other words - how vocab is used in context). When all of this comes together speaking becomes far easier. Listening generally makes up half of a conversation between two people after all, whether that be in your native language or a foreign one.
Some good Spanish podcasts for learners are Espanol Automatico, News In Slow Spanish, Notes in Spanish, etc. There are also some good youtubers out there, like Luisito Comunica for example. Just a side note though - if your problem is with basic conversation, then listen to audio with everyday vocabulary. If your problem is with a more specific subject like travel and culture, listen to audio on that.
I think the key is listening to the same podcast/audio file multiple times until you understand the majority of it - this helps when you can find a transcript to look up words you don't know. Olly Richards has a good article on this, and at the end of the article he has a link to a free listening course: https://www.iwillteachyoualanguage.com/blog/listening-practice-con
Alex Rawlings also has a great method that I've been using with language exchanges recently. Sounds really simple, but it's so so effective. All you have to do is pick a topic (for instance hobbies) and then make a mind map with every single question you think you'd get asked, along with your response - all written in your target language of course. Once you familiarise yourself with the questions you'll be asked, and have a rough idea of your response, it makes reaching conversational fluency so much easier.
Hope this helps!!!
A few tips.
- Ask the other person to speak "lentamente."
- Watch Spanish speaking shows at your level. I can't understand the Spanish speaking news channels but at least I can understand the really dumb drama shows meant for high school student level conversations.
- Expand your vocabulary in context. Listening to a phrase and memorizing is one thing but I found that using the phrase or word in a sentence that is commonly used allows me to understand a greater proportion of what is said when it pops up in an actual conversation I am having.
Keep at it. I have the same problem. Not a native speaker so to me, Spanish speakers sound like they are firing off a machine gun of vowels and consonants. Probably not going to understand their machine gun talk speed for a while.