After being frozen multiple times in my early days, earning NP was a difficult process. Until I got a little better at my favourite games
It took me 2 and a half years (on and off on Neopets) to earn 1.7 million NP ~ to which PPTers benefitted from after my fiance and I called it quits for a while. More recently after returning to the site, it took me a little under two weeks flat to hit 1 million NP.
My ways to earn NP are simple:
Games
Find your niche (favourites) and play them everyday.
I manage 10 - 15k a day alone from my faves.
RSing
Believe it or not, I didn't do ANY RSing before I left Neopets - that entire stockage was from Quest items, Games and Rare Item Codes over a 5-month period. A couple of rare Shop Wiz finds put me over 1.5 million NP within days.
I do restocking every fourth or fifth day now, when I manage to accumulate some spare time. What put me over the million NP mark was a Bludberry, restocked from the Tropical Fruit Shop. Bought at 10k and resold for 120k. 110k profit isn't bad for a beginner
Haven't been able to get very many UB's for a while now since the competition for them went up, but I manage. I usually restock within the wee hours of Saturday/Sunday morning (1am - 4am AEST) when my insomnia refuses to let me get any sleep - I do manage some rare pizzas and plushies during that time.
Shop Wiz/Auctions
As Morningstar pointed out, Shop Wiz finds are surprisingly common. My fiance picked up a Jetsam Transmogrification Potion the other evening for 45k, resold for 215k the same night (putting him over the 750k mark). Enter random things like negg, a random colour, omelette, potion etc - you're bound to find someone selling something for WAY cheaper than everyone else. Codestones, Dubloons and Faeries are also found through this method.
Auctions are a little harder, but I've found at around midday and early evening, you can snipe just about anything of value. I've managed two r87 stamps, 3 petpet beds and various rare books from the Auctions. I don't do this often, though. I do it when I get slightly bored by RSing/Shop Wiz hunting, and I never hold more than 10k on hand - as RE's of varying degrees often strike me unawares (like today with that blasted Kadoatie RE ><)
That's how I earn my lot ^^
Oh and Rare Item Codes - those are fun if you want to take a solid gamble at something. I once sold a Queen Fyora (TCG) when it had just appeared onsite and made 500k out of it. Which reminds me...I need to get some of those booster packs today...*goes to gamble away her soul XD*