pmcollectorboy: This all seems very basic, but it's easier said than done. There's probably way more to this game, and I'm not as clever as some of these other coding geniuses. If anyone knows more about this game, feel free to add.
PaterAlf: Thank you. I think those were exactly the commands that I used so far and that I understand. But there were some more that I'm not sure about it. I have to look at the manual to remember which ones, but I'm not at home at the moment.
As far as I remember the other command is JRO, which is a bit of an odd one.
Basically it jumps the number of lines of the provided argument. So JRO -1 jumps back to the line above, JRO 1 jumps to the next line.
I didn't often use it except in the later levels but if you really want to optimise your solutions I believe it's very important for that.
You can use it for all sorts of things but you kind of need to plan the values you use to make the best use of it..