Use this as your base.
Most of my texture looks like this in the beginning. I'll show you how to spice it up.
Search google or grab a camera and find a basic surface type. Can be anything really. We'll use this crete texture. I already made it grayscale by going to IMAGE > ADJUSTMENTS > DESATURATE (CTRL+SHIST+U)
We'll copy and paste this ontop and change its layer mode to OVERLAY. To get to your layers if they aren't already on the screen, click WINDOW > LAYERS (F7)
In the upper left corner of the layers window, there is a drop down. Its usually set to NORMAL, change this to SOFT LIGHT and you'll see what it does. It should look like this.
It's cool, but not nearly complete. Patience.
Next we will contrast it so that it look right when lighting hits it. Right now, it feels light.
In the layers window, select your grayscale overlay. Press CTRL+J to clone it. Or, on the menu bar, click LAYER > DUPLICATE LAYER and click OK.
With the clone layer, change it layer render mode to OVERLAY and it'll automatically and naturally tone your texture.
Difference
Looks like this when its lined up.
Now its really cool, but we're still not done yet.
The Left and right edge of your texture are not tiling. To see if they do or not, on the menu bar click FILTERS > OTHER > OFFSET and type in half your dimensions into the number boxes. Half of 512 is 256. This will place your edges in the center.
Puke.
Lets get rid of this.
On the tool pallette, there is a brush called THE HEAL BRUSH. This is your best friend. It looks like a band-aid and its left of the regular paint brush. Click it and Alt click where you want to sample to patch up your seems.
Once your done, offset you texture back to normal and your good to format it!
End Product: