I'm traveling to Singapore and I will bring my usual things plus some other personal items such as books and laptops (all mine and used). Any restrictive items I need to be aware of? Any unusual items in their mind that I need to be aware of? I know I cant chew a gum over there, but would they ask me to pay a tax for some stuff I'm bringing with myself?
While there is the general opinion of Singapore as a country with very strict rules and a lot of police control, it is in practise not really the case. Your bags are very likely not even going to get checked at the airport.
For a list of prohibited items for your luggage, you can check the website of Changi airport. While most are common sense, note some things like replica or toy guns. As for custom fees, the allowance for new purchases is S$600, but your used stuff, such as the laptop you mention, should be not an issue. Take note of the allowance for alcohol if you want to bring in any. You are technically not allowed to bring any cigarettes, but one opened pack is usually okay. Also while you mention chewing gum, bringing in some (unless in industrial quantities), is not going to bring you into any trouble, it is in fact commonly done by a lot of locals.
For a more complete overview, I suggest you go read up on the Singapore page on wikivoyage, which talks about some more specific stuff, such as medication.
Do note that there are very harsh punishments for bringing drugs into the country. Also note that attempting to bribe a custom officer (which might work in other countries), will most probably get you arrested on the spot.