Most models have scoring marks included in the printed sheet but if there aren't any, you should consider doing so on your own wherever any folding is required. Scoring breaks the top layer of paper releasing tension which helps makes a better, more precise and square fold that will stay. You can visually identify which models were not scored because the paper tension makes flat walls look bubbled up and rounded. Even after folding hard and tight, photo paper fibers have a strong tension that will tend to curve itself back to its original flat state destroying your model's looks.
To score you will need a dull hobby knife blade or the back of a new one, a small metal ruler and good lighting. Place the ruler along the fold line and run your knife down that line only once. Push down too hard and you will cut right through it. Too light and you might not even make a mark. Trial and error will get it right.
Do not begin cutting the model out until after revising the entire model carefully making sure all fold lines have been scored. Some models or parts of them cannot be scored after cutting them out.
It doesn't matter if the fold is in or outward. Its will work just as well.
To begin cutting your models out you want to start with a fresh X-acto blade. This will make cutting faster and effortless. Unless you have a strong steady pulse, you might want to use a thin metal ruler for cutting your model out just to ensure all edges are straight. Just watch out for any irregular shapes so you dont cut over them. Also watch for areas marked with a red asterix (*) or inside areas with no color. You'll need to cut these out first before cutting through the external outline. These areas are usually in thin delicate areas. Take special care of these areas while cutting or when folding. they can easily break off if there was poor cutting done here.
Once the model has been completely cut out, you will quickly notice the model lacks firmness and might feel flimsy. Careful at this stage. The model can be damaged if not cared for.
Start by folding in from the outside in. Make a complete fold. Don't worry about the shape or position of the folds yet. At this point you want to make sure all tension on every fold is eliminated. You'll know when you have a good fold because it won't want to fold back on you on its own. After all parts and sections have been folded, you may begin to inspect the actual shape of the model and where the tabs and sections will go. Identify visual marks of positioning for when it's time to glue it together. You're probably excited about your new model at this point, since its finally beginning to take shape!
Don'tnt worry about how fragile or light the model might feel in your hands at this point. It will all change once you begin glueing it together!
One of the most constant questions I get is "what type of glue should I use". I know what type you shouldnt use and I can tell you what I use. Experience will also determine what works best for you.
Do not use liquid or stick glues. White glue for example is too watery and can curl your paper, run your ink and takes the longest to set. Glue Sticks might seem like a better idea but because they are wide, they will be messy on your fingers and other parts of the model that should not have glue on them besides the fact that this type of glue is not strong enough for this sort of demands. Try it and in a couple of weeks you will end up with a model falling apart on its own!
CA or Krazy Glue types are good but you'll need a tool like a toothpick for example and a scrap of plastic or metal to place the glue drop from where you'll be picking it up from. Take the toothpick, dab it in the glue drop then spread the glue evenly on the tab and join the sections together. WARNING: You will only get one try at this with this glue. No chance for repositioning or adjusting and its permanent. I know some guys changed to this method because its faster but not until several other DigCom models of experience on their shoulders. I do not recommend this for beginners!
I do however recommend you go with any GEL type glue. Preferably water based since solvents can cause eye irritation over time. Because it's gel, you will be able to place it and immediately feel it tacky. You have plenty of readjustment time and once you fixed the sections correctly just hold them tight for about 3 secs and you're done! The sections will not come apart and once it sets in another 10- 20 secs. its permanent. There are many gel glue brands out there but the one I've been using for the past 8 years is SCOTCH Scrapbooker's glue by 3M. It does not string, smell and dries completely transparent. If you find a better one, let me know! ;) (image below)
Regardless of the glue you use, the process is the same with all.
You will want to place enough glue on every tab surface but not enough that when you press it against another section the glue will squirt or run out excessively. This is a high risk of staining the printed model. Once you get glue on the print, might as well start thinking about covering it up with weathering cause nothing is removing the glue before damaging the actual color on that surface.
The key to a perfectly square and firm model is the glueing process. This will improve as you go so dont worry if you dont get it right the first time. It took me a couple more tries than I like to admit! Everything wrong on your first model is a lesson to improve on the next one.
Have fun and enjoy the learning process. Look at it on the bright side.. at least you dont need to wear knee and elbow pads with a helmet to learn!