Although most levels in Pet Rescue Saga aren't terribly tricky or finicky, Pet Rescue Saga level 48 is one exception. This level is pretty tricky, although it's not the hardest the game has to offer. It still smells of Candy Crush style "random luck" though. I'll do my best to lay out a strategy you can use on Pet Rescue Saga level 48 to good effect.
The first issue with Pet Rescue Saga level 48 is the two keys you've got to break out of their glass cages. This is complicated by all the metal boxes on this level. There are also several balloons here, which you can employ as you need to. Sometimes they're different colors, which I find makes things a bit easier.
When you can, try to blow the metal boxes up with the bombs, although whether or not the bombs can be broken out of their cages is something of a matter of luck. I'd almost suggest using any spare rocket charges to break the metal boxes and release the bombs to break even more metal boxes, if you can. In particular, you want to make sure you break as many glass bomb cages on the right hand side of the screen as you can - if you don't, they are highly likely to go to waste later in the round, and will do you no good in the home stretch.
Just remember that the # 1 priority at the start of Pet Rescue Saga level 48 is getting those keys out of their glass cages. You may need your rocket to do that instead! It's really the luck of the draw, unfortunately. If you fail to get the keys out, you're almost certainly going to lose.
After you've unlocked both sets of key blocks, you'll come into a particularly nasty part of Pet Rescue Saga level 48. The left side is completely covered in mesh blocks, and the right is completely filled with metal box blocks. You can afford to lose just one pet, and chances are good it's going to be during this section. It's a big boon if you can save all the pets here, though, so that you have one that can get stuck at the very end.
You'll probably need to use your rocket to clear a column on the right in order to give you more room to match. Any bombs from the beginning of the level that ended up stuck on the right side are likely to go to waste at this point - this is all the more reason to break these bombs open early!
Past this point is the bottom of Pet Rescue Saga level 48. There is a set of bombs on the right that you need to get down to the bottom of the screen. That will allow you to clear out any remaining metal boxes on the right and save those pets. Meanwhile, you've still got the remnants of the mesh blocks and all that came with that on the left.
Here, again, you're going to have to get somewhat lucky. If the mesh blocks couldn't get cleared out, or the color pattern at the bottom of the level isn't ideal, chances are you're going to have to try again. If you're lucky, you might be able to get an extra rocket boost out of the blocks down here. The strategy depends heavily on the pattern of blocks you've got, and each time through it's random.
However, using the rocket on the right hand column will give you a bomb that is suspended a bit above the rest of the level, which can be useful for clearing the metal blocks in the next column over.
When it comes to the bombs, try to keep them apart so you can detonate them one at a time - often times you can clear more of the metal boxes if you don't let the bombs detonate in a big chain.