How would you start with a student who has very low skills in English?

first of all I should help my student to understand that he or she has a very low skills in English and encourage him or her to do his or her best next time.
Then I will start by basic things, give him or her more lessons in grammar .also he needs more vocabulary to speak and write .

When a person has very low skills in English, you at first must let him understand the importance of the English language and let him start with the basic grammar functions, you have to keep up with him day by day so he will be able to practice it and improve skills. 

the first thing to do is to make the student aware of his weakness, of course in a way that does not hurt him, and try to express your support and that you will help him improve but he has to make some effort too.
than you may want to start with the easy things for him or even you can give him tasks you know he can do, and make sure to encourage him and reward him when he do it right.
also, you can make him find his mistakes or where he did it wrong,in order to drive his attention to those mistakes so he will avoid them in the future

student has to know that he has no skill and starts learning personal information and basic grammar in english

First and most importantly, that you have to tell the student the he/she has weak language skills and being in such a level is very dangerous, and that you both gonna help each other overcoming this problem.
( This to make him/her knows the importance of what is he/she learning - and a good way to show that you are supportive).
First classes should only be based on something that motivates the student.
In other words, teach him at first the things that could make him proud and eager to learn more English such as " How to introduce himself - how to talk about his hobbies etc..).
Afterward, go deeper, with the consideration that he wont know everything.
Assign weekly report for vocab and try to use them a lot during your class so that he can memorize them easier.
Assign1 basic writing task as well.
Make frequent quizzes to evaluate your student and keep all his works in one file.
Give him simple grammar :)

We should start by very simple grammar rules and very simple activities.

You can always start with level one.
See if the students know the alphabets, easy word, colorful pictures, short easy stories to read.
Let them read and read so they get used to read.
Let them try to talk in English so they can start thinking in English.
Yet do not over dose the amount so they will not be lost.

They should know some basic rule about the correct pronunciation of English sounds.
The basic grammar rules that they can use it in speaking and writing after teaching them some simple words.

Create ―bridge‖ programs that ease the transition to postsecondary education by integrating basic skills instruction (or English language instruction) with higher-level academic content or technical skills training; Dually enroll basic skills students in occupational or academic coursework and their developmental or adult education courses; Contextualize basic skills instruction with occupational skills training or other college-level academic content; Require that college academic assessment be coupled with personalized academic and career guidance so that students can find the best fit for their skills and goals among developmental and adult education options connected to college and career pathways; Promote college-going aspirations for lower-skilled adults and youth by developing pathways, with achievable milestones, from adult education and GED to college enrollment; and Set goals and performance measures that give developmental education and adult education programs incentives to prepare students to enroll in and succeed in college.

This is a natural situation in EFL class room even in a elementary classroom.
A teacher should starts talking using pictures e.g.
what is this? The teacher should use lot of implicatures to talk to students.

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there is no doubt that it's a big problem to deal with students in the same class with different levels .
The teacher should firstly, break the ice and allow his students to deal with him / her individually .the teacher may divide the class into groups and use the communicative activities which give the students more time talking through groups and pairworks and have a choice not only about what to say but also how to say it .
It's a good way to make all students participate even shy one's