Hi, all, newbie here.

What's the most consistent way to earn sP? Or, what do you do personally?

Selling CSC, if you can afford that. Quests give out over 4 mil sP daily with Gold Account. Selling quest prizes will give few mil more daily too. Restocking gives varied results, depending on how good you'll get at it.

Do all your quests, you can make over 1m a day from them (sell the item prizes you get, sometimes you get lucky and get a very rare item!)

doing as many quests as possible on a daily basis is definitely going to be your most reliable source of sP.

on this page, add the "quests" widget to your sidebar and start with shinwa - she'll ask you to do a few quests from the various questgivers, so you'll want to do hers before you've maxed out their quests for the day.

once you've finished that, do as many of the normal quests as you can. i tend to prioritize wizard, saggitarius, and quentin, then do the rest if i have time.

wizard quests reward you with wizard tokens which you can save up so that you can buy things from the token shop when it restocks.

saggitarius asks for expensive items (and you need at least 1.5 mil to do his quests, which you can probably reach just doing all the other quests first) but his raw sP rewards are usually quite high.

quentin has a chance of giving you mage amulets when you complete their quests, which can be sold for about 300-400k each in your shop.

since your account is younger than 6 months, you also have access to sarah's quests without needing to worry about her sP limit (older accounts can only do her quests if they have less than 1.5 mil sP), so those are worth doing as well.

other than that, throw all your quest rewards that you don't want to keep into your shop and sell them.

if you are feeling especially ambitious or concupiscent, you can restock all day. Restocking isn't as profitable as quests, but it's fairly easy and not too time consuming and you don't have to stop at 10 or 15 like you do for quests. After that, there are some games like Burrero Bonanza, Matlal's Jewels etc. that have a nice sP reward compared to time invested.

doing quests, check for item drive item and try to restock that (if the prize is good), recycle beast items (check often)

Going to feel like a parrot here, but I say questing and restocking. Sell the prizes from the quests in your shop (unless you want them, of course). Some games can give you decent sP as well.