At a furniture store you'll pay hundreds for a heavy fiberboard thing that won't last. This solid oak table is cheap, easy, solid, and long lasting. Here's what it looks like when you're done:

Step 1: Rough Outline

This is the table base with rough dimensions. The base is made of oak half-banisters (1.5x3/4"), weighs <5 lb. It supports a 3 by 5 foot by 3/4" solid oak tabletop weighing about 50 lbs, no problem. It sits flat and doesn't budge when bumped.

I got the banisters and the oak boards at a lumber yard. The banisters come 1.5"x1.5" x 4'. I ripped them down the length with a table saw. It's kind of important to use pieces with a 2x1 aspect ratio cross section, because it lets you overlap the two center pieces and still have a place to join them to the sides. Oak is very strong. If you switch to softwood like pine, increase the thickness.

Some detail on making the base:

Draw out your plan for the cuts. I don't provide one.
For cutting the pieces, a chop saw is accurate to < 0.5 degrees and < 1/64" and makes your end cuts a breeze. If the legs are uneven the center can twist and the table will still sit flat. But that internal stress will decrease the load capacity.
Screw & glue* the diagonal legs to the center cross, which in my version is square.
Screw & glue down from the top rails into four of the legs.
Glue the center box to the side walls all at once on a level floor using furniture clamps. If you're nervous about its strength, you can put screws. But I've had this table in use for two years now with just the glue there.

Total materials:

8 pcs ~ 3' x 1.5"x3/4"
2 pcs ~ 4' x 1.5"x3/4"
8 screws
wood glue

*Screw and glue means:

Line things up,
Drill a "pilot hole" (look up the right size for your screw!),
Take it apart,
Drill a "through hole" in the outer piece (again look up the correct size!)
Drill a "countersink hole" in the outer piece,
Put some glue between the pieces
Put in the screw until it's just tight, not killing it. And don't put the glue in until you're ready to do a whole set of gluing, or you'll just torque it out while it's trying to set.

For the tabletop Just buy oak boards, glue and clamp. The tabletop is placed on top of the base without glue or screws.