If you're "bad at putting", knowing if a slope is 1deg or 2deg isn't going to help as much as you think....
Just look around you. What's the general lay of the land? Do you picture what a ball would actually do, or do you just aim right some random amount and hope?
Here's the secret to getting your mind to read greens and figure out the arc that the ball needs to take to get to the hole:
Go to your local putting green when no one is around and bring a 32oz (or 2liter or whatever) bottle of water.
Set up a 20 foot putt that has some break in it.
Look at the putt from behind the ball as you do when you're on the course reading a putt. Now look at it from the other side of the hole, looking back through the hole at the ball. This should give you an initial idea on how much break there is.
Now pour enough water in the hole so you can see which exact direction gravity wants to take the ball at the hole if it has no speed. The opposite side of the cup is the direction from which you want the ball to fall into the hole. That's the front door. With a ball that has very little velocity, this will give you the widest hole for which the ball can fall, which is pretty much the fill width of the cup.
Now backtrack on that line and picture the arc needed to make the ball do that. This should give you a good mental picture of the full arc the ball should be taking and if you're not completely new to golf, you should have a feel for how hard you need to hit the ball for that to happen.
Obviously there are more lines that the ball can take that will result in a holed putt, but as the speed increases, the hole effectively gets smaller because a putt that hits the edge will lip out if it's traveling too fast. In this amazingly awesome MS Paint presentation I have created, the dark red line would be my preferred arc. while someone may still take the lighter red line but have to hit the ball harder.
I always look at a hole and ask myself where the water will flow if it was bubbling out of the cup. I can almost always form a mental picture of the arc needed from that and kinda just go from there.
MOST PEOPLE DON'T READ NEARLY ENOUGH BREAK. It also helps to identify the lowest point of the green before you even get to it. It's easier to see if you're away from the green and it's at an elevated level from where you're standing instead of trying to figure it out while standing on it. Unless the green has a lot of built in tiers and humps, this is usually a very good indicator of the general break of the green. Look for valleys and bodies of water. Looking at the overall lay of the land can make it much easier to see the true break of a green.