For example if you had substitute goods, Coke and Pepsi, then a price increase in Coke would result in a demand increase for Pepsi. The positive relationship for substitutes yields a cross price elasticity greater than zero. If you had complimentary goods, coffee and sugar, than the price increase in coffee would result in a demand decrease for sugar. The negative relationship for compliments yields a cross price elasticity less than zero. If two products were independent of each other then their cross price elasticity would be zero.
Income elasticity measures the change in demand caused by a change in income.
If the product is normal than an increase in income will increase demand, or a decrease in income would decrease demand. So an income elasticity greater than zero represents normal goods and an income elasticity less than zero an inferior. We further break down the normal good into a necessity and luxury good. A necessity has an income elasticity less than 1, yet greater than zero. This means that if your income increase you will purchase more necessity but not at the same proportion as the income increase.