The things you should do to improve your speaking depend a lot on your current level. One thing you can do immediately is apply strategy. We have some TOEFL speaking templates that might interest you! Beyond that, it gets a little trickier. ETS actually has a quite comprehensive set of recommendations broken down by level, which are linked below.
|Speaking about Familiar Topics||Weak||Limited||Fair||Good|
|Speaking about Campus Situations||Weak||Limited||Good|
|Speaking about Academic Course Content||Weak||Limited||Fair||Good|
If you know roughly where you fall in this ETS chart, you should see their full set of recommendations! What follows below is a general set of recommendations to improve your speaking skills. :)
Practice speaking English every day. This can be with a speaking partner or not (though communicating with a real person is fun more fun). You need to aim to produce at least 45 seconds of spoken language at a time and talk as much as you can. This works on your pronunciation and fluency.
Practice talking about well-defined subjects, especially issues relevant to students' lives and academic topics that aren't your specialty. Read articles from campus newspapers, the internet, etc. Also listen to local radio. Focus on media that talks about academic/student issues, as the TOEFL will do this for you. Practice summarizing articles/audio, make lists of the topics being discussed, and practice generating a list of main points.
Record yourself and listen critically to pronunciation and intonation. Try to speak in "thought groups" when you express something. It is difficult to understand you if you speak word by word, but if you can express an entire concept in a fluent chunk, your score will increase. Draft a sample response and record yourself reading it aloud. Then mark the groups of thoughts in your response and read with them together. Compare your audio. You'll be surprised how much this can help you improve!
Study the English media you like to consume. Pay attention to idiomatic usage of the language and different accents or speech patterns that are used. What can you take away from the native speakers' expression? If you can emulate their natural speech, you will sound more natural, too!