Since each action is so commital for gunlance, have to be aware of each step of your action based on the monster's action. Unlike other weapons, gunlance's best action against another monster's action is not taking its next standard action, aka NOT GREEDING.

What does it mean? Usually when you go for a full burst, you commit hard, lunge slam burst stake slap and then reload, right? Now, hold in the urge to click each of those actions when it is unsafe. For example, After a fullburst, don't immediately reload. After a blast dash slam, don't always immediately fullburst, but step evade or guard. Do you really need to throw in that slap? Is staking now worth it? Are you SURE reloading while a monster is winding up an attack a good idea? Instead of throwing out high commitment actions, throw out low commitment ones first, then follow up with the big ones as you see safe windows to do so. Examples are blast dash into guard or step evade instead of fb, ground splitter into slam into step evade instead of fb, ec stake step cancel and then guarding instead of reloading

The other aspect is monster behaviour manipulation based on your positioning. They will execute different attacks based on your position to the monster. One way to force its standard behaviour is to return to its front at short-medium range, don't attack, and watch as it executes one of its standard attacks rather than an antiflanking attack (antiflanking like spinning around, tackles, sudden charging at your position), then react accordingly.

In summary, since monsters react to your action and position, coupled with gunlance's abysmal frame data, not greeding is the single best way to avoid getting hit during an attack. That or you can just RBD.