There are two things you might be talking about. In topography and other formal diagramming systems, there are conventional standards for indicating elevation changes. Affaltar provides some information about that in their answer. If you're interested in diagramming, it would be helpful to know what kind of diagramming, and which discipline you're working in.
The more "artistic" exercise of drawing contours has less to do with execution, and more to do with training your brain. The practice is an exercise in picturing an object in your mind, associating that object with the outline on the page, and then imagining what lines would look like if they were wrapped around it.
The result is that your brain learns to recognize the contours you've drawn, as much as it learns to produce the contours you will draw. This practice of drawing is more about holding a real object in your mind, and representing reality, than it is about providing information about the shape of the object. It's easy for REAL contour lines around a REAL object to produce optical illusions that make it hard to tell what shape the object is. So, if your contours look "wrong" or odd, one reason might be that it's one of those real situations where the contours in real life produce an optical illusion, or are difficult to "read." Another reason, is that your brain is still learning to interpret the lines you've drawn. They might BE correct, but LOOK wrong.
Now, that's a very "artsy-fartsy" answer, so to be a bit more practical: don't forget that your contours should be around a single axis, and they should be the same distance from each other on whatever axis you've chosen to draw them around. Drawing your contours in perspective is also a good way to help the shape "read" more easily. If you're drawing contours in perspective, things can get a little complicated, which is where the brain-training comes into play. Once I get a minute, I'll see if I can upload some examples.
I'll reiterate: This is for drawing that is not interested in being restricted to a particular diagramming paradigm. If you're interested in diagramming, your solutions will be related to the conventions of that particular type of diagramming (e.g. architectural blueprints, engineering designs, topographical maps, etc.). Similarly, if you're wanting to draw a cylinder, directly from the top, orthographically, you're going to have a hard time making it look like anything more than concentric circles.
Aside from those qualifiers, here are some tips and tricks to help make contour drawing a bit more straightforward.
Here's an example of an optical illusion I mentioned.
In this case, we can't tell if the shape in the plane is a bump or a dimple, because there's just not enough information drawn. It's not wrong, but if we add some information about where the viewer's eye is relative to the plane, it will "read" more easily. One way to add such information is with a horizon line, or by drawing in the thickness of the plane's edges, which will give our eyes a clue about where the perspective lines are converging to.
Sometimes, it's tempting to draw contours that following the "cylindrical" shapes of an object, because they're convenient. This is certainly a valid style, and has its place, but as an analytical exercise for practicing, it's not as useful.
Studying the 3D shape of an object is often more useful when restricting ourselves to a single axis (even if it's not a conventional vertical or horizontal axis).
A slightly more exaggerated version of the bump/dimple on a plane. You can see that our contours are made at even intervals, but the curves that trace the bump/dimple end up getting close to each other because of how perspective distorts them. Making the contours an even distance will allow the distortions due to perspective to sell the shape better. Uneven "cuts" make it hard to tell whether the distortions are due to perspective, or irregular spacing.
Some details to pay attention to that will help sell the dimensionality of your contours are:
Drawing in perspective:
Think of your contours flat discs in space. Their shape will change depending on whether they are above the viewer's eye level, or below it. Thinking of discs that are stacked like a column right in front of you, just a vertical pillar: one of the discs far above the viewer's eye level will appear very round. The same disc close to the viewer's eye level, right in front of them, will look like just a straight line. The same is true with your contours. A contour that's around a part of the object far above the viewer will look more like its cross-section. A contour that's closer to the viewer's eye level will look more like a straight line.
For example, with this cylinder drawn orthographically, the curves are all the same shape, because they're not drawn in perspective.
With this cylinder drawn in perspective, the curves that are farther below the eyeline have a more extreme curve to them.
When contours are receding away from the viewer in the right way, one or both ends of the contour may be occluded by the sides of the object. In terms of "line" the contour will simply merge with the silhouette, instead of showing a slight bend.
On parts of the shape that are closer, we may see a slight bend at the end of the contour line as it begins to wrap around the object. We may even see the whole contour altogether.