Certainly not the best way but i sell motifs & crafting mats. Its a steady income, not much but steady (~100k a week)

Averaged over the last 8 months I've made around 720K/week, but that's bound to increase since I've reached a tipping point where I've secured enough stocks of valuable tempers for myself to freely sell the surplus (see #1 & #2) and also because #1 has been expanded from 6 to 14 crafter characters over the course of the period with a 15th coming in about 4 months (I only level during double XP events). So probably the current intake is closer to 900K-1M/week.

1) Daily crafting writs - account for about 50% of my weekly earnings, refined materials to keep them going are relatively cheap, and they also save money in the long run by providing a lot of legendary upgrade materials and surveys; I consider Master Crafting writs a bonus but I've taken steps to maximize the drop rate by researching traits and learning cheap styles (<1K per page/book) even on characters other than my main crafter. That's the profit margin, since material price for writs is already accounted for, amounting to ~30% of their monetary reward on average - ancestor silk ones are actually not immediately profitable since the material is expensive but they are in the long run considering the other drops - and the others have very large profit margins of 80-90% since for consumables the craft cost is negligible. I can do all 14 characters within an hour thanks to various crafting addons, as well as decreased loading time due to SSD install, restricted addon load list per character (ex. I only keep MM active on one character, and the combat related ones on the ones currently active, with the former being by far the biggest culprit), and careful location selection to avoid over-complicated assets (ex. Alinor and Vivec load relatively slowly because they are cluttered and large), as well as optimized paths within the location.

2) Selling surplus items on guild stores - account for about 35-40% of weekly earnings. I usually discount less popular items by 15-20% and popular ones by 5-10% relative to average MM price to ensure they sell fast and I can put more for sale. I sell pretty much everything: overland, Rewards of the Worthy and Battleground set drops if they have the proper traits, motif pages (still have plenty of from the event), already learned blue and purple furnishing plans, low level materials that drop from writs, and occasionally also more popular items such as legendary tempers or BoE sets that are considered BiS if I have no use for them. Purple jewelry sells really well lately, since some impatient people buy it to deconstruct and level Jewelry Crafting. I have found the rewards from doing tier 5 writs (2 characters currently) to be not much better than tier 1 ones (remaining 12) so I'm in no rush to power-level the skill on the latter. It takes an average of 2-3 weeks per character just doing tier 1 writs and deconstructing the intricate items from the others and white, green and blue drops. As for maximizing Master Writ drop rate, in this craft, in the same way I did for the others, it's even less appealing, due to the way voucher value is calculated - they need 10x the upgrade materials but they have similar voucher values as other gear writs, so the cost per voucher ends up as being at least 10x (more like 20-30x due to the fact materials are relatively high priced) compared to others.

3) Quest rewards, undaunted plunder from trials & junk items that are sold to vendors - account for the remaining 10-15%. They used to be more as percentage, and sometimes as absolute value when I did steal & fence a lot, but I don't consider that to be particularly time efficient, since #1 and #2 have become so dominant. But for newer players that may actually account for most of their earnings. I remember thoroughly plundering the containers in the starter town then dumping the green and blue treasures at the Outlaw Refuge in town, to buy my first horse (it used to cost 10K, now it's given freely for leveling) get the first bank and bag upgrades. The two ships anchored in the port of Daggerfall, Glenumbra (starting area for DC characters) are particularly suited to this, since the containers on them are almost entirely unguarded (hence no bounty risk) and the Outlaw refuge entrance is right on the pier.

As for drains, there aren't any significant ones at this moment, I have maximized both bank space and bag space on all characters, the last one still has to train other skills on riding but the others are capped already. I have purchased all 7 storage crates with vouchers and earned the 8th by leveling a character, but I haven't placed them since I haven't needed then, and as a consequence I haven't bought a big enough house; I've set my eyes on the Alinor one and I will probably buy it a couple of weeks from now and that will add another 360 slots to the 3480 already available. There is periodic spending, mainly for buying the last few pages from some motifs. Usually I only buy them a few months after they started dropping, since the price is significantly lower than when they are introduced. Those one-time purchases - house, motifs - cost is usually comparable to what I make in a week, so in the long term they barely make a dent.

I sell motifs and crafting materials in a guild store and to players in chat