After rolling out the dough, immerse it in hot oil and gently apply little pressure on the top surface of the puri while it is immersed in the oil.this helps to puff up. you can add little suji to retain the puffiness for a long time. add little sugar at the timeof kneading so that the poori's will not consume lot of oil.
The poori dough should be harder than the Chappathi dough. And Poori should be made as soon as the dough is prepared. These 2 steps avoid pooris to absorb too much oil.