Get a Gems

10000

Play loaner desk in duel school if possible it gives you 30 gem for the duel

Play loaner deck in duel school

Do loaner decks if u havent done all of them

Restart

Start over

nooo

1. ALWAYS fight LD's. Old skills pop up as gems like what the others have said, but also non-skill chests will sometimes give gems as well.
2. Weekly missions. Do them!
3. Loaner decks. DO THEM!
4. The four gem spots on your map.
(Refer to previous posts) Check them a few times per day. Sometimes the same spot will give you gems multiple times in a day. Just give them time to replenish on gems. (several hours usually. Idk the exact time)
5. Street Replay. WATCH THEM! (Well...you don't have to watch necessarily, just open a match once per day for 5 free gems.)
6. Rank duels (Fight your ass off!) It doesn't matter if you can no longer rank up because you've reached your limit. What matters is your cumulative wins. It will earn you gems every monthly season. (~300 per month)
7. Events. Abuse the shit out of them! Try your best to complete objectives that will earn you gems from whatever event is occurring. (eg. Set Sail for the Kingdom event; you abuse the lottery system for a chance to win gems.)
8. Pray. Pray that Konami screws up, release new characters/stages/maps, or release a new box (which usually comes with free 500 gems to buy 10 packs)
9. Last resort. Become p2p. Lol

free gems and coins! works for me yesterday
http://pintient.com/21Mj

Farm standard duelists for keys. Farm ranked duels for keys. Once you have that going, farm legendary duelists with their optimal farming decks and try to hit skills. When you obtain duplicate skills, you get 15 gems each.

Outside from events and delays to maintenance, this from my 84 consecutive days of experience has been the most reliable method to getting gems. This is assuming you've reached stage 60 and have no more gems to obtain through characters.