Writing Advice
To write strong, clear sentences you must know who or what you are writing about (subject) and what you want to say about them or it (predicate). Your writing will be more interesting if the subject is not the first thing in every sentence you write.
Writing that contains mostly short, simple sentences can be uninteresting or even irritating to read. Writing that consists of mostly long, complex sentences is usually difficult to read. Good writers, therefore, use a variety of sentence types. They also occasionally start complex (or compound-complex) sentences with the dependent clause and not the independent clause.
It is helpful to read your written work aloud. When you speak, you will make natural pauses to mark the end of your sentences or clauses. If there is no corresponding end punctuation mark in your writing, you can be almost certain that you have written a run-on sentence.
If your 'sentence' is a dependent clause, or it doesn't contain both a subject and a predicate, then it is not a proper sentence. You can often detect fragments if you read your writing backwards sentence by sentence, i.e. from the last sentence to the first one. You can usually correct a fragment by connecting it to the sentence before or after it.
A rambling sentence is quite easy to spot. You have almost certainly written one if your sentence contains more than 3 or 4 conjunctions. If you read the sentence aloud and run out of breath before reaching the end of it, you have written a rambling sentence. If your sentence stretches over many lines of writing, you have certainly written a rambling sentence and most probably a run-on sentence too.
If you are not sure whether you have written a good, correct sentence, ask your teacher! And remember: The more you read in English, the better a writer you will become. This is because reading good writing provides you with models of English sentence structure that will have a positive influence on your own written work.