Are there any tactics or tools for matching synergis or is it just skill?

If you take a look at how popular players/deck creators work, it's a combination of intuition about deck synergies and a trial and error process that progress through subsequent refinements.

Take for example Anyfin Can Happen: it's clearly designed to belong in a combo deck, with its high cost and high board impact. So you start from this idea and try to build the deck around it.

One of the first thing you have to ask is: "What is my win condition?"; what is the mechanism that gives you victory? It can be a specific combo or even just a simple "get board control and smash the opponent's face". Usually you try to get a win condition that fits the class you're building: if you try to make a Shaman fatigue deck, you're going to have a hard time, while for a Warrior deck it may be more manageable. Figuring out a good/original win condition is usually one of the hardest parts of creating a new deck, and requires a good dose of skill, creativity and understanding of the current metagame: this is because you have to clearly have in mind how the class you chose works and you should also know how the cards in that class work.

Once you have a clear win condition you have to ask yourself: "How can I achieve that?" Here comes the trial and error part: now you'll have to actually build your deck and test it through dozens of matches to verify that the synergies you're putting in actually work. Take for example the aforementioned Anyfin Can Happen: once you put that card as your win condition, you set your deck on a path that requires card draw (or else you risk not finding the card), self heal (you have to survive until turn 10, or later), board clears (to avoid being overwhelmed by the opponent's board) and the right amount of murlocs in your deck (a board full of Murloc raiders on turn 10 is going to be useless).

The first iterations of Anyfin paladin were clunky because were including too many murlocs or were lacking good ways to clear the board. Once people started including Doomsayers, Pyro+Equality, Lay on hands, and, most importantly, reduced the murloc presence to just Bluegills, Warleaders and Old Murk-Eye, the deck finally found its definitive (and fearsome) incarnation.

Naturally this is just an example, but the thought process usually is similar. It takes creativity to come out with a new deck archetype, but it also takes a lot of work to make it actually ladder-viable.

One final note: if in 75% of the cases you lock your hand with dead cards you may have to reevaluate both your deckbuilding process AND your game plan. The whole deck needs to progress your match towards your win condition, but also it's important the way you play it. The mulligan at the beginning may be the difference between a glorious victory and a catastrophic loss. You can't keep in your hand the same cards against an Aggro Shaman or a Control Warrior, but the only way to become good at this is actually knowing what you're facing. You have to understand the meta, calculate the chances that the player you're facing is, for example, a Face or a Midrange Hunter and change your game plan accordingly.

Since you mentioned creating reliable decks let me give you another advice: don't craft or disenchant any card until the new expansion becomes available. Whispers of the Old Gods, as you probably already know, is going to introduce new cards, while restricting many others to the Wild game mode only. The meta will shift a lot and decks considered solid or at least playable today may not be viable at all when the patch hits on April 26th (27th for Europe and Asia). If you have the cards already available, play with them, otherwise don't craft any new one for the moment. If you want to "have a good start", wait. New strong decks are going to rise, creating one today will not help you in a week.

Aside from a general knowledge about card effects and interplay I can only see two "tools" that help build a synergizing deck:

1. Curve - How much mana will be available to you, is one of the few (almost) fixed values of the game. As such you can predict how much cards of each mana level you will need. Roughly: The cheaper a card is, the more chances you will have to play, the more often it should be included in your deck.

2. Purpose - As you design your deck, allready have a number of plays and counterplays in mind. Now you can gear the rest of your deck arround giving you opportunities to put those combos into use. The easier it is to play a combo, the better the deck will operate.