Reading undulating greens is difficult, but it is a learned art.
The more undulations there are in putting greens, the more difficult they are to putt.
If I am playing a golf course for the first time, and the course has a reputation for having difficult greens to read, I always ask someone in the golf shop if the greens have a prevailing break to them such as away from a mountain, toward a valley or an adjacent river.
When you are in the fairway and approaching a green, watch your playing partners' approach shots when they land on the green to see which direction they roll as well as your own shot.
When you are on the putting green, if you are not the first to putt, watch the roll of the other players' putts.
If I am the first to putt, I look for high and low spots on the green. Your ball will break down the slope.
If there are mounds in the green, you may have a double break. I feel the best way to read undulating greens is from the side.
Reading a green from the side will also give you a better feel for the length of your putt and a better visual of the slopes.
When you are lining up your putt look for the apex of the break and aim straight for that point and let your putt run down to the hole with a pace that will take your ball 12 to 18 inches past the hole if it does not go in.
I like to use maximum break with a minimum of speed for better control.
Remember, fast greens break more than slow greens.