I wish I had a page like this one before I started to build my first plane. I encountered so many issues that I was ready to give up. In one weekend I visited the hobby store three times with questions. The next weekend I went to a local air field to talk with people. At that point I realized that my expectations were totally messed up.

So let me set your expectations. Someone said to me that this is an 'acquired knowledge' hobby. I think most hobbies are in that you get some basic information quickly, and the rest of the time it's trial and error. So don't approach this hobby as something that is quick and easy. While there are a number of time-saving actions you can take (such as purchasing a fully-assembled all-in-one plane kit), the hobby as a whole is not quick and easy. Learning to fly alone will take a number of hours, even if you're really good at console games like X-Box.

DISCLAIMER: I don't make any claims that any of my advice is good and/or accurate. This information is knowledge that I've picked up along the way and has worked for me and/or for other people. If you ruin your plane because of something that appears in these pages, I take no responsibility for it.

DISCLAIMER: The web sites that I refer to are there simply for reference and are in no way, shape, or form an endorsement for the site and/or the company that owns and/or manages the site. I provide these links so that you can see what I'm talking about and get an idea of what to purchase.

If you didn't read through the Tools page, then I'll reiterate it here again. You need to have patience with this hobby. Take your time, learn as much as you can along the way, don't be afraid to make mistakes, and enjoy it while you take it all in.
I'm sure you've seen this in instruction manuals a million times. The warning says, "Please read all instructions before starting to _____". Often times you can skip this warning and simply get right to it. Sometimes you can even toss the instructions and do a great job using your intuition and instincts. I'd suggest NOT doing this with the first few plane kits you assemble. Depending on the manufacturer and the type of plane, the instructions may contain some cryptic hints that, if missed, will result in a plane that underperforms. So, please, heed the warning and read the instructions cover-to-cover before you pick up that screwdriver!
Unless your kits comes exclusively with allen/cap screws and bolts, consider upgrading to these. Flat-head and philips screws and bolts typically are more difficult to tighten down than cap screws/bolts. Not only that, but often you can strip the screw head as you attempt to tighten it down. Cap screws/bolts help prevent this. In addition, if you perfer one size standard over the other, consider swapping the hardware out. For example, if you prefer metric to the SAE standards and your kit provides the latter, you can substitute metric hardware for the SAE hardware.
Purchase a small, cheap volt meter to include in your field box. Make sure it can read at least 12 volts. This allows you to periodically check the battery in your field box to see if it needs to be recharged.
I was told that if you have to store your plane for 2 or more months, you want to put a drop of some special oil in the engine so that the cylinder doesn't stick. Apparently, automatic transmission oil contains the same 'ingredients' and is a cheaper alternative. Simply remove the glow-plug and squeeze a few drops into the chamber. Bear in mind that this is for glow-plug engines only.
Normally your plane kit will include pushrod connectors. Pushrods are usually threaded on one side. The threaded side screws into a plastic connector. The other side of the pushrod will be bent either in a 'Z' shape or an 'L' shape and a plastic connector is used to connect it to the other part (a horn on a servo, for example). What you may notice is that once installed, it's difficult to fine tune the pushrod (for example, in the neutral position, the rudder is not dead center). Using E/Z connectors rather than the non-threaded plastic connector makes it easier to adjust them. One thing to be aware of is that these connectors can become loose over time so check them before and after every flight.
The wings on a plane can fold right up given the right circumstances. I believe every plane kit should include some form of brace, joiner, or dihedral that goes near the middle point of the wings. This is a crucial part of the plane, so don't miss it. If you purchased a kit and it doesn't seem to have this piece, call the shop where you purchased it and ask or go online and search for information on the plane.
Your kit may include collars. A collar is a round metal disc with a hole in the middle and a set screw to tighten it to a rod. These are used, for example, on either side of a wheel so that it still rotates, but doesn't fall off. If the rod that the coller will be mounted to doesn't have a flat spot where the set screw will be tightened, use a small file to make a flat spot. By doing this, you decrease the chances of the collar coming loose and falling off.
Use LocTite or Thread Locker on all mounting screws and bolts. Basically, if the you think that a screw will never be removed once installed, use LocTite on it. Be sure to use it on the screws that fasten the engine mounting bracket to the body of the plane. The vibration of the engine can loosen these screws.
The engine compartment (where the engine is mounted to the plane) may contain exposed wood. Usually the firewall (the piece between the engine and the rest of the plane's body) will be coated with some sort of chemical to prevent the wood from become soft. This occurs because of fuel spillage when filling and emptying the fuel tank. The sides of the engine compartment may not be coated with such a chemical. To be safe, use 30-minute epoxy mixed with some alcohol to thin it a little and 'paint' the inside walls of the engine compartment. This will prevent the wood from getting soft and mushy when fuel gets on it.
When mounting the engine to the mounting bracket, consider replacing the regular nuts with nylon locking nuts. These locking nuts stay put much better than ordinarly nuts. This is a good thing since you don't want your engine falling off during flight. If you can't (or don't want to) replace the ordinary nuts, be sure to use LocTite/Thread Locker.
The instructions for your plane should include information on the throws for the various controls. The term 'throw' indicates the maximum displacement from center that a control such as the rudder should move. For example, the throw for the elevator of a particular plane may be 15 millimeters either way. It's hard to judge this without an accurate measuring tool. Consider buying a tool called the AccuThrow. This tool allows you to accurately measure the throw of all the controls on your plane. It costs about $10 so it's not a huge investment for improved performance.
The instructions for your plane should include information as to where the Center of Gravity or C.G. is on your plane. When you have finished assembling your plane, using both hands placed on either side of the fusalage at the C.G., determine if your plane is balanced. The plane should remain either level or just a slight bit nose/front heavy. If it's not, use lead weights to adjust the C.G. Simply glue the weights to inconspicuous places on the plane and re-check the C.G. The amount of weight needed depends on how far 'off' the C.G. is. Purchase the smallest weights possible so that you have more control over the amount you can add to the plane.
Be sure that the engine you purchase for your plane matches the plane. Installing an engine that is too small or too big will impair the plane's performance. Also be sure to purchase the correct propeller size. Similar to the engine itself, if the prop size doesn't match the engine and/or the plane, the plane will not perform well.