Baby will be sitting totally confidently now, with no wobbles or shakes or unbalancing. His crawling will also be coming along in leaps and bounds; he'll be zooming around very quickly indeed! Although by now he will be able to stand up with some help, he may find it trick to sit back down without a bump! Expect the odd bump or bruise here and there, but give him some comfort and he'll soon be on his way again.
Emotionally and intellectually he'll be coming along, too. He'll be more aware of what makes you angry, disappointed, and happy. He may wake up in the middle of the night and look around for familiar people to comfort him. He'll also begin testing your authority, so once you've set your boundaries make sure to stick to them - what is disallowed today is disallowed tomorrow.
It's now time to start using different warnings for baby, too. Instead of just "no" all the time, use other words with a similar tone to your voice; for example "hot" "sharp" "that will hurt you" etcetera. If he gets angry or frustrated, you must be firm. Rules and boundaries are extremely important now.