Read these important instructions before starting!
The most important thing when printing is to print in the correct size. The best way to print the models is to select the desired file (in GIF format) and to save it to your computer. Then open the file in an image editor and print it at a resolution of 72 dots per inch (28 dots per cm). If you print it directly from your web browser, you will not have control over the print resolution and the printout will most likely be too small. This could make assembly more difficult than intended, because it's harder to fold and glue small parts. If you're not sure how to do this, it is worth taking the time now to get help, since it will save you a lot of frustration later!
Note: the part sheets are drawn at a scale of 20 pixels = 1 meter, or 1/140 scale. If you want to print them at another scale, use the following guidelines. To built your model in HO scale (1/87), print at 17.4 dots/cm or 44 dpi. To build your model in N scale (1/160), print at 32 dots/cm or 81 dpi. In both these cases, of course, ignore the scale printed on the sheets.
The second important thing when printing is to use good paper. Standard printer paper is thin, makes colors fade, and wrinkles when glued. If you use premium paper you will get much better results. Premium paper is thicker (heavier than about 100 g/m2), the colors appear brighter, and it wrinkles less when glued. You can even try using light card stock if your printer can handle it. The end result is noticeably better and worth a little extra expense!
Scoring and Folding
Scoring is used to make folding easier. Before you cut out the parts, prepare the folds (marked by little arrows or described in the specific assembly instructions) by scoring them with a scoring tool and a straight edge. An excellent scoring tool is a "dead" ballpoint pen, one that doesn't write anymore, but you can come up with your own tool. Anything sharp is OK as long as it doesn't cut or damage the paper. It is essential that your score marks be straight and parallel. Take your time in this very important step, otherwise the assembly will suffer and the model will look crooked.
After you cut out the parts, mark each fold before gluing anything (i.e. bend the fold). Do it without rubbing your fingers directly on the fold, because you might smudge the colors. Press down on the fold gently but firmly against your working surface so that the paper bends completely, then bend it back to its proper orientation. You can rub the fold through some other object like a ruler; your finger rubs on the ruler but the ruler does not rub on the paper.
Use glue sparingly. More glue will only make the paper wrinkle and the drying time will get longer. Glue only one thing at a time, and let the assembly dry a few minutes before moving on to the next step. (A quick tip to save time: build several models at the same time, so while one of them dries you can glue another.)