I’m wondering why you would want to teach the future tense in your first lesson. Are you a substitute teacher taking over half way through? If so there should be a syllabus your colleague probably used with his class. Ask to have a look at it to see what has been covered and what activities the students are used to.
As for starting afresh
this article in the ICALwiki has useful tips for first time teachers.
See also in the
ICALwiki the Grammar section to brush up on the Future as well as the ESL Activities and Classroom Techniques section.
You may also want to consider getting some TEFL training. Online courses offer a great training opportunity at entry level. They can provide a thorough grounding in a new career and the right tools to approach a new profession within a manageable amount of time and finances.
Learning which are the most effective teaching techniques, how to maximize classroom time, how to make your lessons useful yet fun, how to target your lesson towards a particular learning group, etc. it is all going to help you become a better teacher.
Of course, reading a few books or researching online will help, but being trained by an experienced and qualified tutor that can walk you through it can only be a good thing.
Good Luck!