That's very good for your first attempt at mapping. I think once you've incorporated some of the advice given in this thread into your toolbox you will have a very promising technique.
Here is one of the tiles I used for the walls (I have four of them). I am really eager to learn how to make tileable textures, so if you have the time and it's not too much trouble, I'd be extremely grateful if you could show me how to do it!
Ok I did it in one minute - its very easy in this case. Remember, we are not trying to make a proper tileable texture (that would tile in width and heigth), only an object that can repeat/be tiled along one axis (in this case, X axis).
a) import image into Gimp. It should be on its own layer and the size of the layer should be exactly the size of the image (in this case 100x20 pixels).
b) LAYER MENU>TRANSFORM>OFFSET. Unclick the chain so the X/Y are unlinked, then offset it by 50 pixels; press OK.
c) use the CLONE tool (never use the blur tool here - disastrous beginner's mistake) and make it c. 5 pixels big fuzzy brush. Pressing control click part of the wall about 3/4 of the way to the right and half-way up, then use that to clone the central black bar so it is gone. It doesn't matter too much exactly how you do this - the object is to remove the Y-axis black bar but leave the X axis black bars.
d) LAYER MENU>TRANSFORM>OFFSET. Unclick the chain so the X/Y are unlinked, then offset it by 50 pixels; press OK. Now save the resulting image.
Check it by FILTERS>MAP>TILE and (making sure to unconstrain x/y axis) increase the X axis by (eg) 500 pixels and keep the Y axis at 20 pixels and press ok (unticking that bloody new image box) and you should get a flawless wall.
Ok, so here's the finished result. The map still has a number of flaws, but I think its time to move on to the next project now. Thanks a lot for all the nice remarks and the help I've recieved, and especially to Jack, who's help has been absolutely invaluable! Btw, I checked out your encounter maps, Jack, and they totally blew me away! Really, really great work!
Also, I tried out the body parts but it didn't look right, so I removed them again, but thanks anyway, Bogie.
Looks good. The number one thing to remember is that while we are all here to help and you'll get a ton of feedback and suggestions the final word rests with you. If you like then that is all that matters. This really came out great I can't wait to see the next one. (And I'd LOVE to hear the story about how all that blood got there...) :)