(by Ciabatta Bread)
Gate placement is one of the most complex areas of Summoner Wars, and one of the most daunting to new players. Unit positioning ideas are intuitive: it’s easy to understand why using more attacks, attacking with more dice, attacking important enemy units like the summoner, and preventing counterattacks are good steps towards winning a strategy game. Gate positioning, on the other hand, is opaque.
When I think of how to place my gates, I usually prioritize them like so:
First, tactics. If there's a play I want to set up next turn, or an opponent's play I want to prevent next turn, I use the gate to accomplish it. These gates serve as 0-cost events that stick around and generate value for the rest of the game. The classic example is protecting your summoner in a forward position, but there's also blocking opposing summoning spaces, trapping an enemy unit for tempo, preventing a flank attack, and more.
Second, faction specifics. What you do with your gates highly, highly depends on your faction and your opponent's faction.
If you're playing aggro with CG or WF, you usually want your gates as far forward as possible. If you're playing against ST, you want your gates diagonal to each other to cut off Chain Lightning combos. If you're playing against SH, you want to prevent your gates from sitting adjacent to your summoner. If you're playing SO, you want your Vine Gates back so they survive, and your normal gates forward to protect. If you're playing PD, you want your gates near your Frost Mages, or in convenient positions for shifting. (Placing them for same-turn Ice Ram combos is a tactical move and takes higher priority.) If you are playing SG, you want gates two orthogonal spaces away from your summoner to set up Carry opportunities.
Third, summoning space maximization. The more summoning spaces you have, the more options you have. The more options you have, the more combos are available, and the less your opponent can control what you do. This is why the "knight's move" placement is so popular; it's the most compact way to give yourself four extra summoning spaces.
Fourth, board control. When you want to place a gate, but don't really know where it should go, consider what your faction wants to accomplish in the game. Factions like the Breakers and like open space, to more easily shift their common units around and use their ranged advantage. These factions prefer edge gates. Other factions like the Vanguards like closed space, so they can protect their summoner and fight in melee range. These factions prefer center gates. Most factions fall somewhere in the middle, so make sure to keep your opponent's faction in mind. All else being equal, I usually default to edge gates, as they control more space through the threat of summoned units.