I guess that what has given me more problem is the grammar, specially with the topics in which you have to change structure, for example the indirect questions, wow what a topic , you'd never imagine how many problems that has caused me when speaking; but fortunately I have a deal with one of my classmates who also has the same problem. we agreed that whenever one of us makes a mistake, the other is going to correct him. Believe it or not, it has been very helpful...
Also, I like to speak aloud and correct myself, when I'm alone. In that way I notice my mistakes and try not to make them again when I'm speaking with someone else... In the following video you can understand why I decided to do those things:
