I've taught ESL for 14 years. That's pretty tough that you don't have a curriculum but the web is full of resources you can use.
You'll want to start with assessing the students English language proficiency. There are a couple of assessments. There is the Woodcock Munoz Language Survey(WMLS) and the IPT. There are others but these are two that I am most familiar with. They will give you an idea of how much English the child already knows. They are based on picture vocabulary, verbal skills, and basic reading and writing ability.
My district has always provided these for the teachers to use.
Secondly, you will want to reinforce basic survival English. I mean classroom vocabulary, colors, numbers, alphabet, days of the week, months, and other themed vocab.
If the students are intermediate to fluent speakers, you will want to work on idioms, multi-meaning words, and begin to focus heavily on academic vocabulary.
Understand that you don't have to speak another language to teach ESL, you simply need to learn how to support the learning of English for students who speak another langauge first.
Here are some sites and web resources