Dominion is by the rules very simple, but the execution can be very complex because of the endless possibilities.
There are is not a "best strategy or tactics" that will work always because every game is different.
The key point for successful players is adaptation. However, there are still some basic tips to be given about treasure management:
Buy Bigger Treasure
This advice is really important for beginners because when you keep purchasing bigger treasure cards, your deck will keep improving every turn.
This will lead that you will be able to buy victory points to win the game.
The strategy "Big Money" do nothing else than buying bigger treasures and then Provinces. This is maybe a very boring way of playing, but successful against new players.
New players don't know the importance of silver and gold as they often are the most important cards on the table.
Why are bigger treasures (silver and gold) so important?
Because Provinces cost $8, you need to have at least $8 worth of buying power in your hand.
But this hand exist of only 5 cards and it's not sure that all cards add your buying power.
Assume that all 5 cards were Copper, then this is still worth not more than $5.
Gold can give you $3 of buying power in a single card. Imagine that you have now 2 gold cards, then you need to have only $2 of buying power by the other 3 cards to buy a province.
To cost of a gold card is $6 which is to high to buy by copper. So, we need silver first to buy a gold card.
Never Purchase Copper
Copper don't cost you anything, so it looks inviting to buy it and add money to your deck.
In general, never buy any copper. It is almost always better to pass and don't buy.
The reason is simple math: You must try to maximize the value of the average five-card draw from your deck.
By that rule, every extra copper card will lower the average value.
Also know that the most best cards usually have a price of at least $6 and even $8. So, you can't purchase them with copper.
So, instead of buying copper, try to buy silver as this will bring the average closer to $10.
Switch from Treasure to Victory Points
While Victory Point cards are dead weight in your hand, you still need them to win the game.
Knowing this fact, I still advise you to buy provinces as soon as possible.
A lot of players wait until they have bought gold, but as soon as you owns this, you must take every chance to buy a province.
Know also that once half of the Provinces are gone, that you should start to buy Duchies or even Estates rather than treasure cards.