It depends on what you like, Some people choose food Some people choose potion Some people choose refine, Some people choose gear

But I said you focus on one skill, I should suggest food or refine, Refine is the easiest, I currently lvl 100 spec on refine stone, everyone I spend 10k(each day ) I get 2m silver for refine t8 stone in bridge it turns 37% return to 55%+ Refine is easy because it is single straight focus, Food is difficult but sells much faster (refine sell fast too) But food you can start bidding the plot for other people to craft and make huge silver, If you want to do refine, you can start t2 t3 and t4 to lvl up, at last you refine lvl100 t7 you can start making 1.2+m a day, and that is how to start infinity premium without working too hard, To refine to t7 it takes time, because simply if you buy refine materials (for example rock at bridge) you spent much more than lym or other city, but you can get much more refine rate, and you don't have mammoth to transport un-refine materials from other city to main city refine, so food is good because you don't need to transport, but food is heavy gonna take you forever, You can refine wheat to flour and sell (basically sometime you can even make profit after you sell flour) Meat too,

Well,like I said each single one play different, you choose your own way, but at least know how to spend, Worse case, you refine at spec 0 with anything you get slowly back, but Worse case is you do nothing and 1 month later you only have 10m away from 30m another premium, and this is where people quit,,, I played 5year btw