I do a pretty successful job of getting to higher Waves on Infinity Time myself so I'd like to add to this guide since it's popped up to the top of the forum again.
My personal approach is to head toward on of the map corners, as noted in this guide; I favor heading left from the spawn area and hanging around there initially. Essentially the idea behind this tactic is to get a position where the Gnomes can mainly approach you from a 90 degree arc, or basically from two directions. being in such a position minimizes the risk of a pack of Gnomes flanking you or coming up from behind.
If you find yourself with Gnomes, or Nemesis, all around you what you'll want to do is select a corner and head towards it, vanquishing Gnomes who are in front of you in the direction that you have chosen. The enemies with trail behind you and eventually start bunching together so that when you reach your new corner position they'll be approaching entirely within your view.
Never stay in a pack of enemies and when you are moving move tactically towards the far end of the map since that area will have a lower enemy presence and the act of you traveling will tend to bunch remaining enemies into packs which trail behind you.
On the Floaty Waves eliminating the Floaty is your top priority but don't attack it blindly; when you use your Special Beam attack your movement slows and any Gnomes of nemesis in the area will be able to overtake you. What you'll want to do is head towards the Floaty and be certain to vanquish any Gnomes in the immediate area as you travel so that you can be assured of at lest a short window of time to use your Special attack on the Floaty. If you can get a clear line of sight on it from a distance that is preferable since the Floaty will fire on you when you get to a certain range.
If you need to get close tot the Floaty the best tactic there is not NOT use your Special Beam attack but to get directly underneath it and blast it with your normal beam while moving in a tight circle underneath it. The reason for this is that while the Floaty cannot shoot back at you while you are underneath it the Floaty will occasionally drop Gnomes; you'll want to recognize when this happens which will be easy since you'll be looking directly upwards you'll see a door open up on the underside. When you see that door open give a count of a couple of seconds and you will want to initiate your close quarters Stomp attack since Gnomes will have spawned directly around you. Your Stomp attack will eliminate some and your constant circular movement will keep the Bashy Gnomes from using their hammers on you too much. The important thing to note here is if you are using your Special beam attack not only is your close quarters attack denied to you but your slowed movement makes you a sitting duck. You also don't want to try this if you already have a pack of Gnomes hot on your trail and in sight already.
I usually target Shooty Gnomes first, since they are sneaky and have really good accuracy even when you are moving but after them you'll want to target any Giga Gnomes. The Giga Gnome is slow moving so you can easily keep him at a distance because his hammer strike does a large amount of damage. He will regularly lower his hammer to fire a beam attack at you; the power up for that attack is easy to recognize and should be your signal to dive into cover. The best tactic is to simply circle a small terrain feature or column so that you are constantly backing around a corner while shooting the Giga Gnome; when you see him power up his beam attack you simply dodge into cover and wait for the beam to stop and then resume wearing him down; be certain to take out any Shooty Gnomes who show up and keep the Bashy and Explodey Gnomes at a distance and take them out when they get close.
On the Gnome King Waves be aware of when he summons reinforcements; there will normally be two waves of them, Gnomes and your Nemesis. Be certain to break off from attacking the King to deal with these reinforcements; at the higher levels if you ignore them spawning in you will find yourself surrounded and overwhelmed when the King teleports away and summons in an Ultra nemesis for you to fight. Keep the King interested in you by zapping him every once and awhile to keep him from trying to Destabilize Time but concentrate on clearing out the reinforcements before going back to inflicting large amounts of damage on him.
With the Singularities, you'll want to learn how they behave as some colors represent a bigger threat than others; the green just wanders aimlessly, the red tracks you relentlessly at a stable speed, the yellow largely sits still until you get too close and then races after you, and so on. Pay attention to the audio cue that one is close; the thrumming noise that they make will intensify as they get closer and if you play with headphones you'll be able to be aware of their positions without having to try to visually locate them.