U dont need to be affraid of negative marking.
If u get it wrong u loose 1 mark but if its right u get 4.
Here are some healthy risks
1.if u r more than 50% sure then dont leave the ques.
2.for physics and physical chem- suppose the digit given in question is 7 then there is a probablity that answer is multiple of 7.
3.for bio- select the odd one out.there are more chances of it being correct.
4.for inorganic-upmost and lower most elements in the periodic table are the answer.exceptions should be learned.more than 90% they are asking exceptions.
5.tips for calcutions-learn some calcutions.