Hello meg2589 and all,
I almost exclusively teach Spanish students, with the exception of some American students who are learning Spanish but this is a different story. I can tell you the most common mistakes and difficulties that we, Spanish people, find when studying English.
The first problem that you mention is the 'false cognates' which we call 'false friends': they are similarly written words or expressions that have different meanings in both languages. The funniest example I can give is 'to be constipated', which I'm sure you know the meaning. Well, in Spanish we have 'constipado' which means to have a cold: not at all the same meaning
The overuse of articles is also a problem. But students learn the rules of when to use it and when not.
As for more grammar mistakes:
- 'Auxiliary verbs': there is no such thing in Spanish, so a lot of emphasis must be put on the use of them. A useful and popular exercise is to change an affirmative sentence to negative and interrogative.
-Third person singular
s in the Present Simple: Even with 18-year-old students, we still have this problem. They simply skip it and we, teachers, must put a lot of emphasis in this simple aspect of grammar.
-Adjectives: 'they have no plural form'. I repeat this sentence thousands of times and they don't catch it. This doesn't happen in Spanish: adjectives have gender and number, unlike English. The same happens with the order: in Spanish they usually go after the noun, not before it.
-Speaking of order...: Word order in a sentence. In Spanish it's much more free, but in English is more fixed. Another point to be taken into account if they want to be understood. Common mistakes are, for example,
Said the teacher that would give we more homework which should be
The teacher said that he would give us more homework Do you see what I mean?
Well, the list would go on and on, but I'm giving you some examples. I don't know if you were looking for this. If I'm right, feel free to ask for more, and I'll post more examples of common mistakes Spanish students make.
See you.