Improving English for research I'm going to start my PhD in an English-speaking country. I would like to improve my English for research (fro writing and speaking). Could you let me know any good ways to do that?
As someone in the U.S. currently teaching a class of mostly international graduate students, I've noticed various specific skills non-native English speakers sometimes have trouble with:


Following spoken English, as during a lecture.
Speaking English comfortably enough to ask questions (or later go on a job interview)
Writing English, first for homework assignments and then eventually for papers.


Before you head to your graduate program, some ways you can work on these skills:


Try sitting in on a course given in English, preferably one given in your field and by a native English speaker.  If you don't have a formal opportunity to do so at your university, then try free online courses with video content.  Coursera, for example, has free course content (as long as you don't want credit for the course) from many big name American universities.
Participate in an English language practice group, to give yourself a chance to feel comfortable speaking before you are in the middle of a class wanting to ask a question.
If you choose to brush up on your language writing skills, focus more on grammar and punctuation than on technical writing.  Almost none of my students show up good at technical writing, whether or not they are native English speakers, and I view it as part of my job to teach them.  Grammar and punctuation, however, although they mostly seem like a distraction when I'm grading exams, can make a difference in whether your future papers or job applications are taken as seriously as they deserve to be.


Finally, a few suggestions for after you get to grad school:


If there is any chance you will ever want to use your English professionally, strongly consider living with a native English speaker, and do your best to find a peer group that is not just international students, especially not just those that speak your native tongue.  Total immersion is a much faster way to learn English then just speaking it in class and my students who seek out chances to speak achieve greater mastery.
If your new school offers ESL (English as a second language) classes, take them.
When submitting papers or job applications (anything official that is leaving your school) take particular care to ask an English speaker to check your English (separately from any technical/content advice.)
Most importantly, if someone asks you to repeat something you say in English, don't apologise or let it fluster you; just repeat it calmly and as clearly as you can.  Keep in mind most of us not only want to understand you, we're in awe of your bravery setting out on a new adventure in a new language.


Best of luck!