what is the easiestway to remember what language technique to use?
like grammar e.g imperative verbs
In reference to verbs, ask yourself what 'mood' the conversation is in, the time, the subject/s and the context. For example. If I were speaking to a friend about something I did last week. The imperative would be used because the 'mood' is factual, the time is past, so I would use the preterite tense, and the subject is I (yo).
However if I were talking to a friend and telling them about what I wished, recommend or doubt would happen to another subject outside of 'yo'...the mood would tend to be subjunctive.
Getting a feel for knowing what 'techniques' takes practice and observation. Spanish, like any language needs to be constantly employed, or your fluency and complexity will waver.
Hope this answered your question.