If you were a winning cash game player, then you should not be as tight as complete beginners should be.
The ICM does NOT say that you should be tight early. You are less risk-averse with 8-9 players left than you are closer to the bubble, and you are less risk-averse in small pots than large. So, your risk aversion at the start of a SNG is very small, particularly when you are playing marginal hands with which you probably won't stack off with one pair. You can verify that the ICM does not tell you to be particularly risk-averse early with my program ICM Explorer. In fact, there are times when you should be less risk-averse in SNGs than cash games because the pots are not raked in SNGs.
One reason to be tight early in a SNG is that you are sometimes 4, 5, or 6 seats off the button. In full ring cash games, you are supposed to play tightly from these positions. If you are used to playing in shorthanded cash games, you may need to get used to how tightly you should play in early position, or after a raise from early position. However, if you are confident that your hand would be a winning hand from that position in a cash game with that stack depth, then it is usually right to play it in a SNG.
If you are very new to postflop play, then you might make more mistakes postflop, and this can turn some winning hands into losing hands. This is why beginners should be tighter than more experienced players. Of course, part of being an expert is recognizing that many hands are too weak to play even if you are more skilled postflop.
Be careful that with shorter stacks, position means less, so you can't be as loose on the button in a SNG as you can in a deep-stacked cash game. This is true when you have 40 bb stacks instead of 100 bb, but it gets more extreme when you have a 20 bb stack and it becomes convenient for players to resteal against a button raise. In addition, you don't have the threat of firing 3 barrels postflop.