When you draw any object, start with the general shape and work your way progressively toward the details. Said another way, add the detail last (and don’t overdo it). In these two demonstrations, note how we start with a light, loose, fast, framework (drawn in blue to represent the work you would do with a non-photo blue pencil), and work into slower and more precise lines as the drawing develops. Click on the first image to start a step-by-step slideshow.
Here is a simple leaf shape. Start by sketching in the central axis (midvein). 
Now block in the general shape of the leaf (long, wide, tall, etc.). 
Add a line to indicate the widest part of the leaf. 
Rough in the shape of the tips using negative shapes. What are negative shapes you ask? See the next slide. 
Negative shapes are the shape of the air next to the leaf. It is easier to see the shape of the leaf contours when you do not look at the leaf itself but the empty air next to the leaf. 
Now you can draw your leaf shape over your non-photo blue lines with a graphite pencil with deliberate strokes as most of the hard work is done. 
Now add a mid vein. Let it fade out before it reaches the tip of the leaf. 
Look at the angle and spacing of the side veins. 
Add a few of the smallest veins to add texture and detail. Stop before you think you are done. 
We will draw this leaf the same way. Start with the general shape, here a wide oval. 
Note the location of the mid-vein. 
These blobs just record the positions and sizes of the lobes. Note that we are not carefully blocking in the edge shape yet. 
Carve in the edge shapes with negative shapes (no I don’t color them in blue, this is just to get them to stand out for this demonstration). 
Now pick up a graphite pencil and lightly refine the edge shape. Here I am getting the angles, not the serrations. 
Now the serrations. Work the tiny toothed texture at the edge. Keep the teeth pointing out toward the tips of the lobes. 
Now the veins. Again, let the lines end before you reach the tips of the lobes. 
Note how each lobe has its own vein that reaches out to the tip. 
Add a few of the minor veins. You do not need to put in every one. Note the angle and density of these veins.