One of the most map-dependent COs in the game, Javier is a Green Earth CO who only truly shines where he can use Comm. Towers.
Javier has excellent defense against indirect attacks; thus, he shines best in stalemates involving artillery and infantry formations. He will most likely lose if he repeatedly tries to trade units with COs with comparable day to day abilities, like Hawke, Von Bolt, Sasha, and others; play to his advantages and try to force a stalemate instead, then save up for his powers.
A well-timed Tower Shield or (god forbid) Tower of Power will render you all but invulnerable to artillery and rocket strikes; use that extra defense to safely advance and get your own indirects into better positions.
Most ot the time Javier will be picked on maps with at least 1 available Com Tower per side; make sure to find a way to capture your Com Tower! However, do it in a way that will not compromise your early funding (do not rush your Com Tower right from the start!) while getting it before your units engage in combat.
Javier with two Com Towers (often referred to as Javier2T) has 120/120 stats on every unit, at normal price, and will therefore be banned on maps with more than 2 Com Towers per side. However, you can take advantage of the threat of Javier2T on a fair map by advancing (with enough units) on the enemy Com Tower. Most foes will fixate on stopping you from getting his Com Tower, allowing you to contest other objectives on the map.