It is really important to check and double check your work for errors in spelling, punctuation and grammar. This can be tedious but it is important not to undermine your good ideas with sloppy presentation. Remember, you need to do your ideas and argument justice and if the person marking your work can't find these clearly because of your writing style you may miss out on marks.
Once you have checked your work for these errors it can help to get a friend or family member to read it with you to pick up errors you may have missed. Reading it out loud to yourself is a great way to see if your sentences are too long or busy.