Don't ever vs Never

I don't ever go / I never go

Either sentence is acceptable. However, be aware that the different forms "don't ever" and "never" usually have slightly different connotations. When spoken without emphasis, "never" is a simple statement of fact. To say "I never take the bus," says nothing about why you don't - it might well be that you just like to walk and the distance is short, for instance. To say "I don't ever take the bus", since you have chosen a more cumbersome phrase, suggests that you specifically avoid taking the bus, and that there is some strong motivation on your part for doing so.

Similarly, when using the phrases as part of a prohibition, "Don't (you) ever say that," is a stronger command than "Never say that," and the first suggests that if you do "say that" then the speaker will be personally upset with you.

At least, that's the AmE way I've always heard it used.

http://ell.stackexchange.com/questions/61610/i-dont-ever-go-i-never-go

Could you tell me the difference between come in and come on in?

There is no difference in meaning. I think "come in" is the most common. "Come on in" may be used more often if the people have been talking outside. It is slightly more relaxed and friendly.

Alternative ways of saying the same thing are "come inside" and "step inside"

I hope this helps.

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"Come in!" is more formal than "Come on in!", and doesn't have the same degree of enthusiasm and pleasure.

"Come in" is what I'd say to somebody I didn't know or like. "Come on in!" is what I'd say to somebody I really cared about, like a close friend or family member.

https://forum.wordreference.com/threads/come-in-come-on-in.320877/

The kettle is boiling? or The water is boiling?

When a kettle of water is boiling, do native speakers say?

The kettle is boiling.

The water in the kettle is boiling. OR

The water is boiling.

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In my family, it would always be "Kettle's boiling - it's your turn to make tea."

All your sentences are correct, but I think "The water is boiling" is not very common, and "The water in the kettle is boiling." is so unlikely as to be non-existent. It's just too long.
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Until it is actually boiling you could say 'the kettle’s on the boil'.

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Interesting, either a kettle or a jug.

Any of your sentences would be appropriate, the jug/kettle has boiled.

http://forum.thefreedictionary.com/postst36195_The-kettle---water-is-boiling-.aspx

This evening vs Tonight

I think different people use the words in different ways.

I'd say this evening for between about 5 pm to 9 pm today. And tonight from about 9 pm today to midnight, or perhaps a few hours into the morning.

A certain amount depends on context, and on the shared habits of the people speaking.

Something like a lecture or a film that starts at 7 o'clock could equally be described as both. But 'tonight' can apply to the whole night (until the next morning), so only this is appropriate for events at midnight or 1 a.m.

https://forum.wordreference.com/threads/tonight-this-evening.1969069/

Look out / Watch out and Be careful

Generally speaking, I would use "Look out!" to warn someone of danger that seems imminent. 

I would be more likely to use "Be careful" to warn someone of potential/possible danger.

We could also say 'Watch out!'

'Look out' and 'watch out' call attention to immediate danger. 'Be careful' is more general and can apply to daily tasks. For example, a jeweler must be careful in his daily tasks. A good chef must be careful in measuring the ingredients. A pilot must always be careful.

Credit: http://thegrammarexchange.infopop.cc/eve/forums/a/tpc/f/340600179/m/783100182/xsl/print_topic

May I follow/see/lift/walk you home?

May I follow you home? This may mean that you've never visited their home and wish to follow them in order to know where it is.

May I see you home? It may mean that you want to be absolutely sure that they make it to their house.

May I lift you home? It is used when someone who has a car offers a ride to someone who doesn't have a car. 

May I walk you home? It is used when, say, a friend, accompanies someone to their home. It is often used by people who are dating. The guy may wish to accompany his partner home. Or vise versa.

https://forum.wordreference.com/threads/may-i-you-home.291416/

Arrive home vs. Get home vs. Come home

He arrived home at 6:00.
He came home at 6:00.
He got home at 6:00.
What is the difference betwen them?

To me your three sentences have the same basic meaning, however "He came home at 6:00." has a more definite sense that the speaker was also there (at home) when "he" arrived. In other words, the perspective is slightly different.

Your other two sentences could be used more easily by someone who is reporting the time "he" arrived, but wasn't actually there to witness "his" arrival.

http://www.english-test.net/forum/ftopic16137.html