Tip number 1... When someone answers you back in Spanish (with a time or number for example), repeat what they’ve just said to you out loud. This gives you more time to process what they have just said (as they do often speak VERY quickly) and it also confirms that you’ve heard them correctly.
Tip number 2... If someone (eg. a taxi driver) doesn’t understand you, just say the key words from what you’re wanting to say instead of trying to form a complete sentence. For example, instead of trying to say “¿Dónde está la tienda más cercana?”.
Just say… “¿Dónde? ¿Tienda?”
If you only know very basic Spanish and your pronunciation isn't the best, they’re a lot more likely to be able to understand key words rather than full sentences. They will still be able to logically work out what you’re wanting to say just from those few words.
Tip number 3... Don’t expect to be able to speak as quickly as a Spanish person straight away! Focus on the correct pronunciation of the words, even if you’re saying it quite slowly, then gradually speed it up as you’re getting more confident.