Are you talking about Minecrafty-like generation?

The world can have hills and valleys. From left to right, the land can slope up and down, you can achieve this by having an empty object moving from left to right spawn blocks and randomly moving up and down. You can spawn trees by making the empty object have a random chance of spawning one. Grasses and flowers can also be added in the same way as the trees.

Are you talking about dungeon-like generation? With rooms and chambers?

Have a starting chamber, then rooms can branch out in multiple ways. Avoid creating too many rooms. In each room, pre-made templates can be used. Having props, monsters, etc.