when finding limits at a number, try plugging the number in first. If that doesn't work, try factoring, using common denominators, or using conjugates. Remember, left and right sided limits must be equal for limit to exist. When approaching infinity, look for the largest exponent. If it is on top, limit is infinity (or neg. infinity), if it is on the bottom, then the limit is zero, and if they are equal, then the limit is the coefficients of top over bottom.