Don’t be discouraged. I think you have a good chance of improving your score the next time (there even was a theory that a person could improve the score even by doing nothing… but I don’t quite believe it).
I’m not really sure whether TOEFL will help you to prepare for SC, since, AFAIK, grammar structure is not a separate part of the TOEFL test anymore. Still, TOEFL could strengthen your overall English level.
As for GMAT - here are some observations from my reading people’s debriefs on GMAT forums. Perhaps, you will find them useful.
1. For non-native speakers, verbal scores in various preparation tests tend to vary more than for native ones. So the factor of luck matters more for them. However, mere luck will hardly give you, say, 45+ in verbal. Technically, if your true ability is around 38, if you are lucky, you have a good chance to hit 41-42… but that’s it (on the other hand, if you’re not lucky, you can equally get 30-32…
Thus, it may be helpful to look at your verbal scores from practice CATS. If they vary a lot (say, from 30 to 45), on real thing, theoretically, you have as good a chance to get 45 as to get 30. Unfortunately, in reality it is more often something in lower 30’s than in middle 40’s… So it seems that only consistent scores in verbal CATs have some predictable ability. Otherwise be prepared that GMAT-verbal will be more of a lottery.
2. In verbal part of test, unlike in the quant one, it is very hard to feel how well you are doing and where exactly you make mistakes. So, perhaps, it was not SC-questions that crushed the score.
3. During the last month of your preparation, DON’T do any verbal questions (SC, CR, RC) that are not from OG or GMATPrep or Powerprep – especially if you are non-native speaker. It will only hurt you.
And the most important thing - don't give up. You shall conquer it
Good luck to you!