I put the images behind spoiler tags so that you can choose to view them when you want and hide them when you don't want them.
Before doing the borders make sure the page is properly rotated and resized. If you resize after doing the borders they become blurry again and you will have to redo them.
If you wish here is the original file for you to practice on...
Select the Pencil Tool (B) which is a part of the brush pallette.
Or you can use the line tool (U) with the anti-alised option unchecked. We don't want to use anit-alise when doing straight lines like borders because then it blurs the effect. We want nice and crisp borders. Just remember to recheck the anti-alised option before doing other drawing work with the line tool on a diagonal. If there is a diagonal border then use the line tool with the anti-alise box checked.
Set the pixel width to 3 px color #000000 (default black) for FMA pages. Make a new layer (CRTL + shift + N) I call this layer borders. Zoom in to around 300 percent and line up the tool with the inside edge of the border on the page. Click the left mouse button and hold down the shift key (holding down the shift key while drawing with the tool insures that the line you are making is perfectly straight), and draw the border across the page. When there is more than one panel with borders aligned I continue on to complete the border without reseting the tool this way I can be sure of proper alignment.
This is a close up after the lines have been drawn.
Notice the line across the text bubble? We will take care of that before we are done. Also notice that the orginal border is still there and making things look messy. We will take care of that in the next step. Now here is the full page with the new borders drawn on. It looks like quite the mess but this is easy to clean up.
To clean the outside of the panels we are going to use the rectangle too. (U). Make a new layer I call it whites and do most of my cleaning of the whites on this layer. Make sure that this layer is postioned under the borders layer. Change the foreground color to white (#FFFFFF) and select the rectangle tool set to fill.
Pick a corner to begin and using the outside of new borderline as your guide extend the rectangle out to cover the outside of the page. You will have to do this in stages to cover the entire page. Here is the page with the white parts cleaned.
Now the extra lines from when you made the borders are pretty obvious what isn't obvious is the two text bubbles that extended outside of the panel. Reduce the opacity on the white layer to around 75 percent and go in and erase the white over the text bubble with the eraser tool (E). Don't forget to return the opacity on this layer back to 100 percent. This image shows the area with the opacity level reduced so that you can see the lines of the text bubbles.
This process is the same for SFX that extend outside the panel borders you just have to erase more. Now click on the border layer and using the pencil or line tool color white over the excess border lines. And erase the borderline that crosses through the two text bubbles that extend outside the panels. What we have left to do is clean the inside of the borders now. You can see from this image there is still some of the old border remaining on the inside of the borderlines.
Click on the white layer again and go in with a brush and clean the inside of the borders where you can if they need it. The page will look like this when done.
All the borders are nice, crisp, and perfectly aligned and all the space around the panels is nice and white. Now all you have to do is finish the clean!
A final note if you have SFX that extends outside of the panel borders there is usually a little white space between the SFX and the borders as if the text had been stroked. You want to make sure and have this white space if your original raw had it as well.