A few points here:-
1) Sorry to say this, but you really need to improve your own English! You will never be effective as an ESL teacher until you do that.
2) Telling your Ss not to worry about about grammar, tense, and word order is a double edged sword. It may help them to relax a little now, but it is only a matter of time before you find yourself trying to remove all the bad habits they get into now. Don't pull them up for things you haven't taught them, but if you have taught them, for example, present continuous make sure they use it - don't teach it to them and then tell them it doesn't matter!
3) I am presuming you have monolingual classes. Getting Ss to speak English when they can communicate much better in Thai is very hard. To get round this you need situations where they have no option, or it is more fun to speak English.
Role play is one way. Get them to act out situations in English. They can be made up, taken from a newspaper, from the internet, just about anywhere.
Closely related is plays. I would suggest modern ones rather than Marlowe or Shakespeare! If they are up to it, translating local plays/legends/stories/etc. can be fun.
Word games. From my own experiences with Thai students these are often the most effective. There are a lot of games around, and a quick search on the net should bring up plenty.