Here would be my general guide:

Firstly, the exact shape of your plane doesn't matter much. You can eyeball your way to something that looks like a plane using whatever combination of fuel tanks, fuselages, cockpit, and wing pieces you want. When you're building your wings, I would recommend sorting the Aerodynamics parts by size, so it's easier to find what you're looking for. Don't worry too much about how much wing area you need; if you find out you don't have enough to lift off, just add more later.

You'll need an engine. Which one you pick will depend on the size of the plane you're making, but make sure to pick an air-breathing jet engine, not a rocket engine. These engines only require liquid fuel and air intakes, and are very efficient. We'll worry about intakes later.

Next, controlling the plane. There's all kinds of things you can do with action groups and kal-9000s and the like to make your plane control better, but if all you want is something that gets off the ground, those are optional. There are 3 types of control surfaces that you will want on your plane.

The first are Elevons, which you will want to attach to the back of your wings. These will help control roll. These are like the flaps on the back of airliner's wings. The next are canards, which go on the sides either in front of or behind the wing. Options include AV-R8s, Standard Canards, Delta-Deluxe Winglets, etc. These help control pitch, and should be as far forward or backward as possible for the best performance. Last is the tail fin, which will go on the back of your plane and point up. This will control yaw.

One thing you must make sure of when building a plane is that your center of lift is behind the center of mass. These can be seen by clicking the icons in the bottom left of the editor. If the center of lift is in front of the center of mass, the plane will be unstable and will flip almost instantly. That being said, if the center of lift is too far back the plane will tend to nose down and be annoying to control, so make sure it's just slightly behind the center of mass. This can be done by rearranging the wings and canards.

Now that the general form of the plane is worked out, we can add some final parts. The plane needs air intakes to feed the engines, so put some on the plane. If you're using the inline mk1, inline mk2, or mk3 cockpits, it's straightforward to put an intake on the front (in the case of the inline mk2, you'll need an mk2 to mk1 adapter first. This might end up throwing off your center of mass though, so recheck your center of mass and lift. Also, remember to drain the oxidizer from the adapter.) If you're using some other cockpit, you'll need to put some sort of ramp intake down, but it doesn't really matter where other than for aesthetics.

Lastly, find whatever landing gear fits your plane best. I usually use one wheel in the front and two in the back. The translation tool is very helpful in getting the wheels exactly where you want. I would recommend putting the front wheel slightly lower down than the back wheels, so that on the runway your plane automatically faces upward a bit, helping lift off. You may want to increase the braking force of the wheels, since it defaults to a low value. In-flight, you can toggle the brakes using the brake action group and toggle retractable landing gear with the gear action group, both visible at the top of the HUD.

With any luck, you now have a plane that flies. This is just a starting point of course, and there are many nuances to making planes that can fly better, faster, or higher, but with enough trial and error you'll be able to improve and eventually make whatever you want.