So many students of Portuguese worry about getting small things wrong, and in all the classes I have taught, two of the most common questions from beginners are about 2 things:
1 - When do I use obrigado and obrigada?
2 - When do I use por favor and (se) faz favor?
I always say these are not hugely important, and in fact are often used interchangeably by native speakers (so adding to the confusion of learners!).
A couple of points: For obrigado/a, you rarely hear the ending of the word. Por favor and (se) faz favor when they mean please are very similar.
Want to know more? There’s a very nice video here from RTP about obrigado/a (and inho/a). Listen to how the man pronounced ‘obrigado’ at the beginning of the video - can you hear the end of the word? And there’s a good article about por favor and se faz favor here
However, there are two things that learners don’t take on board from the beginning, and if they did, they would make better progress:
1 - Pronounciation, particularly no being noooooooh (like the Scottish)
2 - Masculine and Feminine, did you notice it’s DUAS coisas? not dois. This is not so tricky in Portuguese, as the correct forms usually end up rhyming :)
Food for thought! If you need any help with your learning, do get in touch :)