Level 49 is a short level. There is only one line of bubbles above that which you can see at the beginning. That, in fact, can be a problem. I’ve cleared the bubbles more than once without getting the necessary points for that precious first gold star. I’m recommending getting any potion that will add to your arsenal if you have the coins for it. It will pay off in the end.
My suggestion is to try not to let the infected bubbles out of the center area if you can help it. (Sometimes they just divide themselves on either side of the 2 diagonal rows of black bubbles, not much to do then, or is there a pattern…?) If the infection does get away from you, at least don’t let it go lower than the lowest black bubble or you might as well just practice wall shots until your ammo is gone, because the ceiling will never show up.
Ordinarily we recommend clearing the sides so you can do wall shots. Not this time. Go up the center, being mindful of the infection, and angle toward the inside walls of the rows of black bubbles instead, with your goal being to nip off the infections at their roots, above. You have a generous allotment of 4 higher lines of bubbles to make your kill shots into.
As usual, be conservative with your shots and consider each one carefully, but don’t always go for the clusters unless you have green spiders waiting. It’s way too easy to miss getting that first gold star because you couldn’t resist knocking down a big cluster when only blue spiders are waiting. Level 49 teaches chess-like consideration of moves, big time.
3 Star Video:
Basic Strategy Video by Jorge: