- Being confused about ser/estar
“Soy aburrido” is different from “estoy aburrido” - one means “I’m boring”, and the other “I’m bored”. “Estoy triste” doesn’t imply the same as “soy triste” - the first says “you feel sad” (now) and the latter means “you are sad” (always). Messing up these two Spanish verbs - both translate to English as “to be” - might get you into some trouble, or at least be misinterpreted.
- Calor and caliente
“El té está caliente” is a very innocent Spanish sentence that means “the tea is hot”. Some foreign speakers then overuse the word “caliente”, e.g. “está caliente” when they really mean to say “está calor” ([the weather] is hot). On hot Summer days, foreigners have also been known to say “estoy caliente” instead of “tengo calor”. Caliente is an adjective, not a noun! So when you’re saying you’re “caliente”... you’re saying that you’re, hmm, excited.
- Forgetting the plural
Cuales, quienes, cualesquiera, every single adjective there is, pronouns… Almost everything in Spanish has a plural form. Forgetting that it exists is a portal to broken Spanish sentences, e.g. ¿Cuál son la camisa roja? instead of “cuáles son las camisas rojas”. If you’re learning Spanish seriously, this is definitely one of the things you should pay attention to.
- Not using the right prepositions
Spanish has a lot of prepositions that might sound the same to foreigners. However, to us they imply completely different things. Saying “pienso en ti” (I think about you) is not the same “pienso por ti” (I think for you). Acing the prepositions is key to make yourself understood, not to mention speaking proper Spanish like a native! Just as foreigners struggle with in and on in English, Spanish students have the por vs para challenge.
- Confusing time with time with time
“What time is it? You ask that question many times and you make me waste my time.” Don’t attempt to translate this word for word in Spanish. In the first question you should ask “qué hora es”, and during the answer you should say “preguntas eso muchas veces y me haces perder tiempo”. Tiempo can also mean “weather”, by the way. If you’re an English speaker, learn this carefully - otherwise nobody will understand you!