The hardest thing to get balanced in a Dominion hand is the number of action cards to the number of actions.
If you never gain an action card, you will end up with one action wasted on each turn because you had no action card. That is a little bit unbalanced, but it is very easy to build a deck which gives you much more unbalanced hands.
One possible strategy
If you during the game gain only a single action card and it is one which does not give you any extra actions, then that will be slightly more balanced. You'll often have a wasted action, but every once in a while, you'll draw the action card and be able to use it.
Taking that strategy further
But this only allow you to gain a single action card during a game. As soon as you have gained two such action cards, you can get hands where you have shifted the balance too far. You will sometimes have a hand with two action cards and only one action. If the action cards are some that draws extra cards such as two
Smithy cards, then the risk of this happening is even higher.
You can try to counterbalance this by buying the
Village from the original game or one of the variants from the later extensions. But you'll get more unbalanced hands as now you will often have a hand with a
Village and only a single other action card to play or none at all.
Even if your deck overall is balanced in number of
+2 Actions cards to action cards with no extra actions, the individual hands will not be balanced. If you take this strategy you need to ensure that the action cards you do buy are valuable enough to justify the unbalance that they inevitably will cause.
Another possible strategy
If you only gain action cards which say
+1 Action, you will keep the slight imbalance between actions and action cards you would have with no action cards at all. This means you will always have the needed action to play any action card on hand, and you will always end your turn with one wasted action.
This strategy is likely going to beat the strategy of buying 0 or only 1 action card during a game. In particular if the choice is between buying a
+1 Action cards of cost 5 and buying a silver, the
+1 Action card is likely a better strategy.
Beware of cost 3 and cost 4 cards with no extra actions
There are many action cards at cost 3 and 4 which will give you two coin and something else, but no extra action. The something else may look compelling enough to make you believe that this card is more valuable than a silver. But often that something else is not valuable enough to justify the risk of having the card on hand with no actions left. The
Chancellor is one example of a card I would avoid.
Any strategy can be undermined by some combination of kingdom cards
Whatever strategic advice you read about Dominion, you should expect that some kingdom card exists, which will undermine that advice.
A strategy of only buying
Province can often beat beginners. But that strategy becomes a lot less efficient if the
Pirate Ship is in the game.