To me, the gravedigger scene seems more about offering the audience some comic relief in the midst of some difficult and emotionally heavy scenes than it does about building suspense. It functions like a little "breather" of sorts. Certainly, the audience knows that danger awaits Hamlet, especially after the conversation between Laertes and Claudius where they plot his death, and so this delay in the graveyard creates some suspense because we are waiting to find out what's going to happen. Further, we know that Ophelia is dead, but Hamlet does not, and this creates dramatic irony: a really common way for playwrights to create suspense. We don't know how he will respond when he finds out, and—based on the conversation between the gravediggers that begins the scene—we understand that Ophelia is about to be buried. Hamlet is going to find out any moment. There is also a great deal of wordplay in this scene, and this helps to prolong it and heighten the audience's sense of expectation. The gravedigger, for example, makes lots of jokes and then speaks so literally with Hamlet about the grave he's working on that Hamlet and Horatio have to retrace his language in order to ascertain his meaning.

Shakespeare uses several different methods to create suspense. One is simple and nearly universal: being in the presence of death makes most people edgy. More dramatically, several plans or activities are still in suspension. We don't know if Laertes is going to move on Hamlet, if Claudius has another plan, and/or if something related to Polonius' body will happen. More directly, the diggers discuss if Ophelia will get a Christian burial or not (if she was a suicide, this was not likely), and Hamlet wonders about the identity of the body uncovered there. All these combine to leave us anxious and wondering.

What means does Shakespeare use to raise suspense during the fencing match?

William Shakespeare builds suspense by having Hamlet refuse to drink from the poisoned cup even when he's won points on Laertes and is supposed to drink. The audience gets more and more on edge as they wait for him to be poisoned from one source or another while he refuses to drink and avoids the blade.

The biggest source of suspense is the poison. The audience knows the cup and blade are both poisoned but not when—or who—will end up actually receiving it. Since Laertes is the better fencer, Hamlet gets three chances to strike Laertes. This actually means that there are more rounds for Laertes' blade to poison Hamlet. In case that doesn't work, though, Claudius also plans to poison his goblet. He says:

If Hamlet give the first or second hit

Or quit in answer of the third exchange,

Let all the battlements their ordnance fire!

The king shall drink to Hamlet’s better breath,

And in the cup an union shall he throw

Richer than that which four successive kings

In Denmark’s crown have worn.

What means does Shakespeare use to raise suspense during the fencing match?

Shakespeare gives advance warning to the audience about the complexity of Claudius' plan.  If the fencing scene were to occur without any of the additional information, the only suspense would be "who will be hurt"?  However, adding the poisoned tip and the poisoned cup add more drama to the scene and offer more possible outcomes, which increases the suspense.