Hands on activities, repetition, illustrations, ect. Anything authentic is helpful when learning a new language.
Also, these websites will most likely be useful to you:

google translate and www.daveseslcafe.com

Making them generate language is most beneficial to them. It's much better than filling in blanks on worksheets. They need to be writing and speaking with you as much as possible. For example, have a conversation or a little interview about a topic, such as, (generic example) "What did you do last night?" or "Describe someone you admire. Why do you admire that person?" Prompts depend on their level, of course. While they speak to you, write down some of the grammar errors they make, and then go back over the errors together. Make them tell you the information again, using the corrections. You can do this in a written fashion, with sentences or paragraphs. This is just one activity, but you should research some ESL sites online. Personally, I think your best resources are other teachers. Ask them what's been working for them. Adopt the philosophy that using English, and not studying English, helps them improve more than anything. Studying helps them some, but using English helps them alot.
PS I have to disagree that translation is best. It's not. Translation should be a last option. That just keeps them thinking and using a first language, and they will continue to hesitate and stumble as long as they continue to constantly think in and translate directly from their first language. Translation is a crutch. Sure it makes things easier sometimes, but it's a crutch nonetheless. My students who rely on first langauge dictionaries and translators all the time have the hardest time communicating. Some teachers think you can't always instruct in the target language, but I do it all day, every day, and I have many adult students who buy into the same philosophy I have (as well as the other teachers at my school) and they excel.

English as a second language is best learned by experience and hearing it. Television has constant speaking, so that's an option. The students don't really need to know perfect english; who speaks perfect english anymore? I think it's best if they learn the meanings of words and phrases and how they sound.

Go to a bookshop and buy books about conversation and others.
Don't buy complicated stuff, because you want to have fun.

Try to tie the lessons to their own experiences. As a student teacher, that is one thing that they are always telling us. Also, make sure that they are understanding the message. They may not talk to you, but make sure that they undderstand what you are saying.

There are a whole lot of ESL idea and teaching sites. Search on ESL in Google.

If you're fluent in Spanish the best thing to do is to translate to them. Also, use flashcards. It's a fun way to learn things and everyone can pitch in with pronunciation. Worksheets are great too. Specially those explaining verbs and nouns. Go over them at the end of class. Also, you could have skits dealing with real life scenarios. For example, at the grocery store, the bank or their kids' open house.