Plenty of sun, good moisture, not too fertile soil, ample spacing.

Hmm.... Maybe my soil is too fertile. Would that lead to overly sharp taste, or not much depth of flavor?

nygardener - what kind of soil are you using for your arugula?

I'm assuming you've tried different varieties? There are plenty of alternatives. You may find one that suits you better.

I haven't tried that many varieties. I've used a few different brands of seed for "typical" arugula (the type that looks like what you buy in the store). I tried a rustic arugula one year, but I honestly had much the same problem with it (too spicy, not enough deep taste). It was in a completely different location - different property entirely. I'm truly losing faith in my ability to grow the stuff well! The plants look good, but....

Plenty of sun is not necessary. Try to grow sylvetta(sp?), wild arugula, much sharper taste and deeply lobed leaves.

I've grown regular arugula in full sun in garden soil that's amended with organic compost and a little bone meal, and it's done very well and tastes great. The soil is on the clayey side and the climate is cool; those may help. In any case, it tends to bolt in the heat, so I usually plant a few times during the season.

Do you have a spot that's not actually in your garden to grow it?
Mine 'jumped the fence' ages ago and happily grows and self-seeds where it likes. If it's in my way, I eat it!
I have very limited bed space and like to keep it for things that want attention. Arugula is fine pretty much left to it' own devices.

I amend the garden beds with homemade compost, but don't use any fertilizer with cool season crops except beans. Never had a problem with arugula. I don't understand your description of spicy, but no flavor. Sounds like a contradiction.

Wow - bunch of new responses. Where have I been?

nygardener - I wonder if the clay has something to do with it. I've heard that Arugula has a lot of calcium in it. Maybe it likes a more minerally soil? When you buy it at the store, there tends to be some sand on it, but I don't generally add sand to my soil (which, last year and this,is mostly mushroom compost).

Feijoas - None of my arugula has jumped ship. I let a lot of it go to seed last year - the flowers actually tasted better than the leaves- but I don't seem to have any volunteers anywhere.

Natal - Some arugula is spicy but also has a deeper, rich green flavor. Some arugula is just spicy, but not much else. Or at least that's what my tastebuds think.

Glib - I did grow sylvetta one year. I agree with you, it has a sharper flavor and it looks pretty too. But I still didn't achieve arugula nirvana.

For the first time since planting arugula for years this batch is tasteless. Doesn’t have the pungent peppery taste at all. Is growing abundantly in the same soil used before. I added some composted soil though to freshen it up. It was from a new seed pack, labeled ‘organic’, Ferry Morse brand.
Very strange. The only diff was adding the extra compost soil to the top layer.
I think I may pull it out and start over with new soil. We are addicted to fresh arugula as what comes from the store in a clam pack is slimy and turns yellow. Overpacked. I used to get it from an Italia grocer and it was big leaves, with the root still on. It was the best for flavour. Can’t fine it anywhere.

Commercial growers focus on milder varieties, because it's probably what a lot of consumers want. You can try Astro: https://www.fedcoseeds.com/seeds/astro-organic-arugula-3020