check please

1.Don't step on the grasses,it spoil the garden.
估計是告示才會以現在式文法出現。見議
No walking on grass. (it spoil the garden 不用了)，並用告示標語插在草地上。

2.Here's our itinerary for Friday.
這句O.K.

3.Don't forget to flush the toilet.
和第一句相似, Flush after use 並用告示標語貼出

4.I am going to a youth centre to take a course.
I am going to take a course at the youth centre.

5.I want to inprove my maths.
typing mistake of inprove, should be improve.

6.'Let&# 39;s go to take a course' suggest Yoki.
描述式多用過去式來表示
"Let's go to tak a course," Yoki suggested.

1. Dont step on the grasses,
It spoils the graden.
OR
Don't step on the grasses,
otherwise you will spoil the garden.

2.Here's our itinerary on Friday.
OR
This is our itinerary for the activities on Friday.

3.Don't forget to flush the toilet after use.
( you only flush the toilet after you use it )

4.I am going to a youth centre to take a course.
(correct)

5.I want to improve my maths.
( the spelling of word "inprove" should be changed to "improve")

6."Let's go to take a course", Yoki suggests.
(Yoki suggests = active form)

"Let's go to take a course", suggested by Yoki.
( suggested by Yoki = passive form.
The full sentence=
"Let's go to take a course" , which is suggested by Yoki.)

1. Don't step on the grass or you will spoil the garden.
( [ IT ] refers to stepping on the grass but it is ambiguous (不明確) in the sentence.)

5. I want to improve my maths.
(improve, not inprove)

6. 'Let's go to take a course,' suggests Yoki.
(Note that it is a comma [ , ] after course.)
(suggests or suggested , not suggest for a third person singular subject)