You are not alone!
My GT 1.9 mJet diesel is the same.
First make sure that the "green light" is there on the battery top. If it isn't, there's your first problem. All batteries deteriorate over time. The trouble with modern batteries like those in the GT is that they are supposedly "maintenance free", and it is difficult to top them up with de-ionised water. In addition, the top of the battery is inaccessible without removing the electronic gubbins and the leads from the top, which can cause disconnection problems for the radio and the car electronics etc.
If your battery shows green then it's OK and there's a problem somewhere else; glowplugs probably in this case, or even starter lead connections.
If your battery shows black, then a long run should charge it up so that it shows green. If it doesn't, then it's probably time to change it if you want to be safe. Mine's like that at the moment, but I haven't yet got round to doing anything about it.
If your battery shows white, then there is insufficient fluid in it and it should be topped up (difficult - see above!).
Provided there is a reasonable charge in the battery (ie it started and ran the day before and hasn't been drained by any other electrical stuff) then operate the glowplugs several times before operating the starter motor (up to four should be enough). In other words, the glowplug indicator on the dashboard should light up briefly when you turn the key as usual, then the key should be turned off and back on again so that the indicator lights again and then goes out, for as many times as it takes (but you probably know that already! /
With luck when you finally start the thing the combustion chambers should be warmed up sufficiently so that the car starts and you do not get a nasty cloud of clag out of the exhaust pipe. Presence of clag at this point would suggest that you have a depleted battery, or one or more of your glowplugs is defective, or the leads to the glowplugs need attention.
All this could be avoided if car manufacturers could be persuaded to fit batteries that at least could be inspected, opened up and maintained properly. Unfortunately that is too simple!
Hope this helps