Theory:

Some basic things about sentences.
They must start with capital letters.
They must finish with full stops, question marks if the sentences are questions, or exclamation marks if the sentences are exclamations.
They have to have a verb.
They have to have a subject which is always a noun.

The simplest sentences have a subject, a verb and an object of the verb.
For example:
David (SUBJECT) plays (VERB) football.(OBJECT)

A verb can have a DIRECT OBJECT or an INDIRECT OBJECT.
A DIRECT OBJECT is a noun that follows the verb.
It can be identified by asking who or what receives the action of the verb.
For example:
David plays football - David is the subject, plays is the verb and football is the direct object.

NOTE: You cannot put another word between the verb and the direct object.
For example:
He plays VERY WELL football. - IS INCORRECT.
He PLAYS FOOTBALL very well - IS CORRECT.

The INDIRECT OBJECT gives more information about the verb and the DIRECT OBJECT.
For example:
David plays football in the park. - IN THE PARK is the indirect object.
It is always a noun, often has an article, and is connected to the direct object by a preposition.
For example:
I bought a hat for MY SISTER (INDIRECT OBJECT) in London yesterday.

This is the safest way to structure a sentence:
It has a SUBJECT (I) followed by a VERB (bought) followed by a DIRECT OBJECT (a hat) followed by an INDIRECT OBJECT (my sister) joined to the direct object by a PREPOSITION (for) and finally followed by two ADVERBS (London) and (yesterday).

Generally, adverbs can move around in a sentence, but when together, the order of the adverbs is important - MANNER, PLACE, FREQUENCY, TIME and PURPOSE.
For example:
David swims enthusiastically in the pool every morning before dawn to keep in shape.

When constructing sentences in english, the best way to avoid mistakes is to
start with the subject,
add the verb (make sure the correct tense is used)
add the direct object
and then all the other pieces in the order explained above.
For example:
I play football with my friends in the park everyday in the morning to keep fit.