Write short sentences then. There's nothing wrong with that.

Keep your sentences short. For example; When I do written English, I often just use simple sentences. It is terrible, but I don't how to express myself. You are expressing your self ok as I can understand you. Do written exercises every day and listen to English programs so that you can hear how sentences are formed. http://www.italki.com/knowledge/page/IMPROVE%20YOUR%20ENGLISH%20LISTENING%20SKILLS.htm

hi Nancy, don't be upset with that, it's natural for a beginner to experience such hardship. all you've got to do is to practice a lot. there's really nothing wrong with composing a short sentences as well as selecting a simple vocabularies - for as long as they understand what you're trying to convey. anyway, this is how we start to learn - learning the basics! :)

That is because you need to improve your grammer and vocabulary。learn how to use composite sentences like attributive clause，adverbial clause，subject clause。But don't try to make unneccesary long sentences, what I emphasize is if you can just use one sentence to explain the meaning of two sentences, then do it.

I would say: "When I write (in) English, I usually only use simple sentences. It is terrible, but I don't know how to express myself well." dont worry, my chinese is the same! I agree with Liz. Practice learning more conjunctions （連接詞）, they are the most basic way to create more complex sentences from simpler ones. More practice will make it very natural for you to create longer sentences! Keep it up! 加油！