There are a gazillion and one websites for ESL lesson plans and tips. The info is overwhelming. I recommend two things: First, become a really good, effective teacher. You can do that by getting certified as a teacher (online https://www.teacherready.org/, use me as a reference please! University of West Florida, 12 hours toward Mast. in Ed.) or by at least reading the books below and applying the research-based, evidence-based principles in your classroom. Even if you are not a certified teacher, the info below will turn you from a chic/dude with a business degree who's teaching English in Korea, to a stellar, effective teacher that engages your students!
(If you are not interested in becoming a good teacher, and only came to Korea for the pretty Korean girls and to get drunk, please, stop making the rest of us look bad and go home or grow up.)
Second, look on You Tube for videos specific to lesson plans, grammar, ESL, etc. Teaching in Korea is great, whether at a hagwon (private academy), public school, business, or university. Enjoy the life of living abroad, travel Asia, experience new cultures, and become a great teacher and evolve as a person!
My professional; portfolio has great links, resources, and books on education for you!
Suggested Reading for all Educators!
The First Days of School, by Harry K. Wong
Who's Engaged, by Janet K. Pilcher
...is moving to South Korea to teach English, fulfilling a dream of many years.