What hannah said plus.
Leave one space after every full stop/period [UK/AMERICAN] before starting the next sentence, the same for commas and after punctuation. You can leave two stops after Full/ stops/periods, but this is difficult on computers were often the computer removes the extra space in the background and is not seen very often today because of this.
Start each sentence with a Capital letter. the pronoun I should always be a capital. I readily admit I am not as good at this on a computer as when I hand write, you don't have to hold down an extra finger on the paper like you have to press another key and then release the key each time on a computer.
Try to divide your writing into smaller pieces or paragraphs every time there is a change in the topic.