Type in UCS then OB (for object). Select the inclined line. That's it. Now to reset the UCS, type in UCS then W (for World).
Another way is to use the Parallel Osnap Option. While drawing the required line, SHIFT + Right Click and select the Parallel option there. Now move the mouse over the inclined line and you'll get a Parallel Marker. Done! Now you can continue with the parallel line.
Moreover, you can even use the Offset command. It involves less steps than the others and is more "flexible".