Basic condensed idea - keep the tune running in your head, even when you can't get it out on the whistle.
In my amateur sessions that I play in (usually for fun with friends, nothing too serious), there are times when either the tune I'm trying to play gets a bit too quick/complex, or I fumble a part, or one of the other musicians makes me laugh* and I can't continue. If I'm not the only melody line, this isn't too much of a problem, because someone else is probably continuing the tune and I can jump back in at the beginning of the next part.
But, if I am the only melody line, and I can get control of myself fairly quickly, it's <i>very</i> useful to be able to keep the tune going in your head and know what notes are next. A way to practice this is to play a practice tune on the whistle while thinking about the melody in your head...and suddenly stop playing, but still think the tune. Practice jumping back in and staying on the right beat/note. It's easiest to start out jumping in at the beginning of the B part, or the second half of the A - standard places like that.
Next, work on leaving a note or two out (room to breathe!) and continuing on from the next note.
If you are accompanied by only bodhrán, as long as you keep the beat you can pretty much restart from anywhere. But if you've got a guitar or something along with you, their chords are dependent on the melody line (as I understand it, not being a string player).
The tune must go on! Even if you flub the middle, if you can make it to the end, people won't remember the flub so much.
* At Tom's session, in mid-tune, the bodhran player announced "Hey, I'm facing north!" sounding quite pleased about it. It's *really* hard to keep a straight face sometimes, in my group.
<font size=-1>[ This Message was edited by: avanutria on 2003-01-06 17:31 ]</font>
You gotta love those percussionists! he he he!
Maybe then it's time to learn a new tune.