Read some of the articles on this page, they are all talking about Data Sufficiency:
https://www.beatthegmat.com/mba/gmat-data-sufficiency
As for personal strategies that worked for me,
(1) know what type of question it is. there are 2 types: (1) asking for a value (2) yes/no. Knowing which type of a question it is has proven very helpful. I know what i am looking for through the question. for (1) you are simply using the 2 statements given in DS questions to get a value. for (2) you are using the 2 statements to get a yes/no answer. remember here NO doesent mean that the statement is insufficient, but NO is a right answer. It is right because the statement was sufficient in determining the "NO" answer.
(2) use the AD/BCE grid. This is very very helpful! If you know A is insufficient, cross out A and D. If A is sufficient then cross out BCE because the answer must be AD.
I hope this helped a little!
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
- Alfred A. Montapert, Philosopher.
