Having a dictionary on hand is a great way to improve your vocabulary. If english is your second language, buy a combination dictionary which has two sections, one in your native language and the other in english. A good start is to choose about five to ten new English words to learn each and every day. Make sure you keep a list as you go along and continuously review your list. Even if you just learn a few words a day, your vocabulary will increase by at least 1,000 words in only a year! If you are using a combination dictionary, make sure you look for words you already know in your native language that you have no idea how to express in English. You will find that this method can really improve your english skills quickly.
When improving your english skills, a grammar book is very handy. You will find that there are a number of fantastic grammar books available. One example is Strunk & White's 'Elements of Grammar'. Another great grammar book to use is 'Essentials of English', which not only covers grammar, but also correct usage and even punctuation, with separate sections which will teach you how to improve clarity in your speech and writing.
Correct ordering of words in a sentence is called syntax. This is usually one of the most difficult areas to master in any language. In order to improve english skills in this area, start by studying the parts of sentences in detail. You will need to practice and get the help of a skilled native english speaker to improve your skills.
You have probably heard of what is called language immersion techniques, where someone is put amongst people who speak nothing but the native language. You will find that through repetition, imagery and demonstration, people will pick up on the language in a very short time, at least to a conversational level. Start by trying this with friends and make sure to ask for feedback.
Last but not least, sign up for an english course. There are a number of ways that you can do courses these days. It can either take place in a classroom, through an email course, distance learning or even through online video seminars.