I agree 100% with all Dave wrote.
I'll add to that that. In a busy pile-up it's well worth just spending a while monitoring the range of frequencies where the DX is (or might be) listening. This gives you a better chance of dropping your call into a clear frequency.
Also, I have seen it written by a well respected DXer that he suggests you avoid trying to find the last used frequency on the basis that's what many others will be doing, resulting in a flood of calls all on top of each other with no chance of the DX being able to pick one out. Spreading out seems to be preferred.
And lastly, I'd suggest a delayed call every now & then...just to try and give your signal a shot at some 'clear air' once the general hubbub subsides. Worth a shot.
Dean - G0RIF http://blog.dean-barnes.com/
-- A recent RTTY convert with 107 confirmed