There's a way to make a brush "Fade Out" as the stroke continues. Almost like a real paint brush would.
Select a basic brush with your "Preset Picker." About 25 pixels or so would be a good size. Now, click on the "Brushes" tab on the upper right of your Photoshop working space ( or hit F5 ).
Click on "Shape Dynamics" and make sure Size Jitter,Minimum Diameter,Angle Jitter, and Roundness Jitter are all set at 0%. The Controls after Angle Jitter and Roundness Jitter should be set at "Off." (As Shown Above)
Now, next to the Control under "Size Jitter", click the small arrow on the right and select "Fade."
In that small box to the right of it, put in a number, somewhere between 50 and 300. Depending on how long your line is. This value is how many pixels out you want the line to go before it starts to fade out completely.
Now take the brush and paint on your canvas. You'll see it "Fade Out" as it goes on. What it's now doing is becoming smaller and smaller until the brush size is 0 pixels.
You can also make it actually fade out. Instead of (or in addition to) clicking on "Shape Dynamics," click on "Other Dynamics" under the brush tab menu.
Set everything to 0% and "Off" as before. Under the "Opacity Jitter" slider, change the "Control" on that to "Fade." Now, in the small box to the right of it, put in a value like you did before, 50 to 300 pixels, or as long as you need it to be. This works the same way, but it will actually fade out, instead of getting smaller, and actually I use both settings.
They both have their own different uses, but also work very well together.
Well, hopefully you learned something new here, and you may want to keep an eye out for more Photoshop tips in the near future.