I assume you're using the pen tool
I also assume you have approximately no idea what you're doing.
So here's a quick and dirty and by no means comprehensive guide to using the pen tool:
The top line is what you're doing.
The bottom line is what you should be doing.
To get lovely bezier curves you'll need to use the following tools:
I've highlighted the wrong thing here, you'll actually want the direct selection tool -- the path selection tool selects whole paths, while the direct selection tool can select single nodes.
Using the convert point tool, click and drag on any node that doesn't yet have a curve on it and you'll get a pair of handles:
Don't use the convert point tool on a node that's already got those handles, because it'll remove them, and you'll have to do it again.
If you want to adjust the curve on an existing line, you use the direct selection tool, grab one of the handles, and manipulate it until you get the curve you want.
Keep in mind: you can drag the handles independently of each other. This is useful for if you want to bring a line to a point.
General pointer: avoid using the "stroke" option, because it is
absolutely hideous. For one, the idea of using the pen tool is to achieve clean vectorised line, and the stroke results in raster data. For two, it's
absolutely bloody hideous.
Compare:
To achieve the righthand curve, I used my best of all best friends, shape layers.
This'll make a vector-based layer mask based on the path you draw. You'll notice in your layers tab, a "shape layer", rather than a conventional raster layer.
First, a pointer. Don't start dragging points around and applying to curves until you've thrown down a basic shape, thus:
(Also, make sure you close off the shape by clicking on your first node once you've drawn the rest of the outline.)
Once you've got your rough shape
using as few nodes as you think you'll need, you can start messing with curves:
This should illustrate how few nodes you actually need to use to create a shape.
Fewer nodes make for a smoother curve.
Incidentally, if you think you've got a node where you don't need one, make friends with this:
Lastly, have a bean.
Delicious.
(I managed to miss a point on the bottom there, twice, woops)
This is to illustrate how I'd personally approach the paper mario style: rather than faffing about with outlining the bean separately, I made a black shape as my bottom layer, and then drew the blue shape on the top, using the techniques I mentioned above.
As should be obvious,
work over a sketch It makes it much easier to check your lineweights and the shapes you're laying down if you've got a sketch to refer to.