The most basic type of sentence is the simple sentence, which contains only one clause. Another term is “independent clause”. This means a “sentence that can stand on its own” (only one independent clause--usually one subject and one verb).

A simple sentence can be as short as one word:

Run!

Usually, however, the sentence has a subject as well as a predicate and both the subject and the predicate may have modifiers. All of the following are simple sentences, because each contains only one clause:

Melt!

Ice melts.

The ice melts quickly.

The ice on the river melts quickly under the warm March sun.

Lying exposed without its blanket of snow, the ice on the river melts quickly under the warm March sun.

As you can see, a simple sentence can be quite long -- it is a mistake to think that you can tell a simple sentence from a compound sentence or a complex sentence simply by its length.

The most natural sentence structure is the simple sentence: it is the first kind which children learn to speak, and it remains by far the most common sentence in the spoken language of people of all ages. In written work, simple sentences can be very effective for grabbing a reader's attention or for summing up an argument, but you have to use them with care: too many simple sentences can make your writing seem childish (although you'll probably score higher on grammar).

When you do use simple sentences, you should add transitional phrases to connect them to the surrounding sentences.