It's pretty simple.
You just need ground beef (keep in mind that higher fat content beef will be more moist but will shrink more -- I like using leaner beef as it's less greasy), ketchup, egg, spices (Lipton onion-mushroom mix works great), and a binder (i.e. breadcrumbs).
I have never in my life actually measured out ingredients for meatloaf.
I just use enough beef to fill a loaf pan (my mom likes to use a 9x9 square pan). Put the meat in a bowl, add ketchup till moist, mix in one egg and packet of seasoning, and enough breadcrumbs to where the mixture isn't loose and sloppy.
Bake at 400F until done.