Do you find it difficult to apply the grammar rules on the ACT English section because wrong answers "sound alright" to you? That's the down side to the English language: spoken English and written English might as well be two different languages! In speaking, we tend to slur letters and words together -- "I shoulda gone to the party." We use slang to communicate ideas -- "Dude!" We leave prepositions dangling at the end of a sentence -- "You wanna go with?" And sometimes we don't speak in full sentences, ignore pronoun references, and misplace modifiers.
Applying the grammar rules in context can be helpful because we can check to whom a pronoun refers, but it can also lead to errors brought on by application of sloppy speech to formal writing.
Here's a way to remove your "ear" from analysis of grammar rules and focus on reviewing the rules themselves. The SAT (and PSAT) give discrete sentences with several word groups underlined. The test taker's task is to observe and analyze each word group for adherence to the same grammar rules used on the ACT. You can use retired SAT or PSAT tests to practice identifying the rules without the distraction of a whole story.
I use retired PSAT tests, which are available for $3 on the College Board Store website:
You'll need the answer key as well, but that's free and is provided as a download on your computer. A word of caution: my Apple computers do not recognize the format of the downloads, so be sure to have Word or some similar way to open the answer keys.
An added bonus is that you will get the entire test, so why not practice Reading and Math while you're at it? The Math concepts stop short of the knowledge level required on the ACT and Reading uses a different success strategy, but the practice can't hurt.