Get plenty of rest
Eat a good breakfast (if you're hungry during the test it can distract you and you don't need that to happen)
Go over all your notes
Also during the test if you have any multiple choice question use the POE strategy (Process Of Elimination)
If you have a short answer question use RACE. RACE is a strategy that I was taught. R - restate the question. A - answer the question. C - cite evidence. E - explain.
(I don't exactly know what the staar test is but I think a friend of mine said that it's like a state standard test.)