Obviously, don't spend shekels on unimportant shit. Avoid the temptation of getting cosmetic shit and entering events that don't pay for themselves (unless you really, really want to, who am I to judge).
If you're starting out, the priority is to get as many useful cards as possible and obviously, quick and premier draft give you the most bang.
Buying boosters at 1k shekels a pop is inefficient, because dropping 5k on quick draft will give you more or less the same number of rares AND gems on top of it. Discounted boosters at the store are fine, so get those.
Start with the 5k quickies, upgrade to the 10k drafts if you feel confident you can win at least 50%. If you're only winning 0-2 games, stick with Quick drafts.
Watch some draft vids to coach yourself, if you don't draft that much, it's sometimes difficult to break habits from constructed. It's always a bit of a gamble, so I like to save up for more than one draft entry.
Take it slow, there's no get money quick scheme in this game. Your daily earnings are capped at something like 1500 geld, depending on which quest you rolled, so take your time re-rolling all the 500 ones.
There's really no point in going for 15 wins/day unless you're really having fun, otherwise you'll burn out quickly.
The only option to make more shekels in a day is by entering events, but that requires a top tier deck or a good feel for the meta (not to mention luck) to get anywhere.
Also, try not to blow the whole bank in one go. They sometimes give nice deals in the store (discounted draft entry token, gems for gold) and you'll be a sad panda if you miss those.
It's fine to just sit on a 20k or more before you decide where to invest it best.
