1) First of all start games that are easy for you, for example: Advert Attack, 200m peanut Dash, Chia Bomber 2, Dubloon Disaster, Extreme Herder, Flycatcher, Jubble Bubble, Meerca Chase II, Mootix Drop, Petpet Rescue, Rink Runner, Trouble at the National Neopian, Typing Terror, Volcano Run, Whack-A-Ghost, Whack-A-Staff-Member and many more in Action. (Note that you can only play these games 3 times a day.)
2) Invest in stocks; start with cheap stocks because they are most likely to make you money. They can reach to the price of 15 to 20nps per stock.
3) Get rich items from Mystery Island; Tombola, Lost Desert; Coltzans Shrine, Maraqua in the Maraqua ruins, Underwater Fishing.