The word like should never be used before a clause.
Example 1 (incorrect usage): It looks like it will rain.
Like should only be used before a noun, as in the following example:
Example 2 (correct usage): The girl looks like her mother.
Take a close look at the two sentences above. Do you see the difference in how they are used? In the first sentence, like is followed by the clause it will rain. In the second sentence, like is followed by her mother. Whenever a subject and verb follow, remember to substitute like with either as though or as if, as illustrated in the final example below.
Example 3 (correct): It looks as if it will rain.
What about
“looks like rain is on its way”
a common expression.
Here “like” funcions as a preposition with “rain” a noun (which is grammatically correct) but “is on its way” part of a noun phrase (hence grammatically correct) or is it a subordinate clause (incorrect)?.
Of course, many people just say “It looks like rain” which is wrong if the “like it will” is implied, but is grammatically correct since it like is modifying the noun rain. “The dust in the air was so thick it looked like rain.”