Some choices seem strategic, but actually lack information that the player would base their decision on.
My gangster game once had three dice you could roll. One die got you money, another attacked the other players, and another gave a variety of useful effects and bonuses.
So, what's wrong here?
With the first two dice, you can plan out a strategy involving them. With the last die, you don't know what you're going to get, so you can't plan anything.
To fix this problem, I increased the strength of the last die. However, the strategy remained the same. If you were winning, you'd roll this die, because it was good. And then, you'd probably be winning by even more. If you were losing, you had to formulate a specific plan, and roll one of the other dice.
Despite the last die being complex, the strategy ended up being too simple.
These days, there are four dice, and each does a very different and
specific thing, with no overlap.
Avoid benefits that make a player just generally stronger. Examples would be allowing the player to draw extra cards, or just granting them more income, in a game where the only resource is money. If the benefit is too broad, one player just feels generally stronger than another, and continuing the game seems pointless. And, for the stronger player, there's no new strategy created.
The Radlands card Muse gives you an extra water (the game's basic resource) each turn, so you have 4, not 3. This just leads to the player with Muse playing more stuff. It doesn't matter what it is. The extra volume of stuff will wear the opponent down. They just have a simple, numerical advantage. (Radlands people can be easily killed, especially by a skilled player who knows to kill Muse, so it's not a big problem. I still wouldn't design a card like that these days.)
In Agricola, you start with two family members. This means you can take two turns per round. You can get a third person. That just makes you generally stronger, as you can then get more of everything.
"More turns/actions" is the most general benefit there is, and I recommend avoiding it.
Instead of general strengthening, make a player significantly stronger in one specific way.
Near-future benefit is good for a game. It ties the turns together.
In both Magic and Radlands, you can't use your characters the turn they enter play. You have to wait until your next turn. You don't exactly know what you'll want next turn, so you have to intuit it.
If a benefit is too far in the future, it can become too general, and be stripped of its strategy.
Radlands had a camp that allowed you to damage something, on your next turn. However, multiple cards will have likely entered and left play by then, so your damage is likely going to go somewhere you can't possibly anticipate. Doing damage is still good, but it can only be evaluated as "a damage" versus its cost, as you don't know what it's going to hit. It just became a general benefit.
In 7 Wonders, the first round is all about collecting resource and trade cards. However, these are really only important in round three, and somewhat in round 2. Round one is still an interesting puzzle, but it's very self-contained, because you don't know what's coming in later rounds. Rather than build up a big plan, you just collect a variety of resources.
The "exploration" mechanic lets you go to an unexplored area of the map, and see what's there. It sounds fun, but why would you actually do it? Even if there are bonuses in there, you don't know what they are. You just have to average them all out, and step into the unknown.
Many abilities will require that a certain condition is true. Then, you get the benefit. There's a lot of design space and depth in conditional effects.
However, it must be a condition that you can control. If it isn't, then you're just receiving the benefit randomly, and that's not strategic or interesting. There's little difference between "gain 6 dollars when your roll for the turn is 6" and "gain a dollar each turn". Another example is a magic sword that works better against elves, but you have no control over whether you'll be fighting elves or not.
An incidental benefit is one that you gain, without choosing to do so. You just gain it when you do something else, or it's an obvious benefit that you might as well gain.
Incidental benefits aren't the result of a strategic choice.
In my gangster game, there's a police cordon that can
surround some locations. Being inside the cordon also protects you against
the Drive By action, which is on one face of the red die. Players would
sometimes go inside the cordon, but protection against Drive By was
never the reason why. Drive By was only one face of the red die, so
wasn't likely to be rolled. Players would sometimes be protected from
Drive By, by the cordon, but it was just an incidental benefit. Drive By
was supposed to be a cool effect which players could avoid, by hiding
inside the cordon. It turned out to just be a more complicated and
random version of regular damage.
I added Drive By to a second face of the
red die. Now, it's twice as common, so you can expect a tangible benefit
from hiding inside the cordon, which makes moving into the cordon factor
into your strategy.
A choice is also not a choice if it doesn't make you change your strategy.
I added "Dens" to my gangster game. You put your den on a location, and every time you go there, you get an extra benefit. The problem is that you go to locations based on what you wanted to achieve. You got the extra bonus from the Den, but it didn't mean anything, or influence your decision.
A very common source of incidental benefit is where an action gives more than one benefit. These extra benefits will usually not factor into the player's strategy. That's fine if you're just trying to balance, but if that extra effect is supposed to be interesting and strategic, then it will fail to be so.
Some actions don't have consequence because they're too similar to other actions. It doesn't really matter what the player does.
In one of my prototypes, players moved to various locations in a town, collecting different types of cards and bonuses. One would give you one each of four different cards/bonuses, while another would give you two each of two. Another would give two of one type of card/bonus, and one each of two others. In this way, I could make a whole lot of different and interesting combinations, and I could make the cards/bonuses given match the theme of the location.
I explained the rules to players, and they understood them easily. They went to have their turn, but were immediately bewildered. They had no idea what to do, so they just picked randomly. This continued for many turns. They couldn't parlay this rainbow of options into any kind of concrete strategy, so they just "collected stuff", because more stuff is obviously good, and that's all they could deduce.
The options in your game — whether they be cards, board spaces, or any kind of option — should be as distinct as possible. They should have a distinct purpose, and achieve that purpose to a significant degree. Avoid options that grant the player a basket of advantages.
A player should be able to see a clear and obvious path to their objective, and take an action that points strongly in that direction.
One of the locations in my prototype was the Karate Hall. You could go there and pick up three Attack cards. This location was unusual, in that it was focussed. It was actually the most useful location in the game. When you decided you wanted to attack someone, you went to the Karate Hall, and got exactly what you needed — Attack cards. Now, all the locations in my game are like Karate Hall.
A more important feature of distinct options is that they give players control over their strategy. They can easily get the tools they need. The skill is in choosing their grand strategy, not in trying to scrape together and manage incremental amounts of resources to fund it.
Distinct options, which do one thing, might be less interesting on their own, but they make for vastly better gameplay. Actions should only overlap in function, with good reason.