I'm not very knowledgeable, I'm afraid, Lumpee, but for what it's worth - I check calories first, then look for added sugar, but am not extremely fussy - I recognise that most chutneys, for example, are going to have a bit of sugar. I don't think sodium is a problem for me, so I don't check that.
I don't actually count calories - for example, I'll eat a carrot or an apple without think about calories at all - but things that come in packets that make it easy to see how many calories are in it per one - as in the crackers I eat as an occasional snack are 115 calories for seven, according to the packet - then I'll use that as a guide as to whether to have it or not.
I avoid very sugary things, like a Snickers bar, but that's more for teeth than for diety reasons.