Answer

When performing an attack, all applicable attack bonuses and penalties (such as +A effects) are applied to the base attack value before drawing an attack modifier card. If there are multiple bonuses or penalties, the party chooses the order in which they are applied.

This means:

• The order in which you apply bonuses and penalties can affect the intermediate attack value before the attack modifier card is drawn.
• After all bonuses and penalties are applied (in the chosen order), you then draw and apply the attack modifier card, followed by shield, ward, and brittle effects.

Steps (from page 25):

• Apply all attack bonuses and penalties in any order chosen by the party.
• Draw and apply an attack modifier card.
• Apply the target’s shield bonus.
• Apply ward and brittle conditions.
• The target suffers the resulting amount of damage.

Example

If you have a base attack of 2, a bonus of +1, and a penalty of -1, you can apply them in any order, but the result will be the same (2 + 1 - 1 = 2). However, if there are effects that multiply or otherwise interact, the order could matter.

Source: page 25

Summary

The party chooses the order in which multiple attack bonuses and penalties are applied to the base attack value, and this is done before drawing the attack modifier card. This order can affect the final damage if the effects interact in non-additive ways.

Source: page 25

Source: Core Rulebook (pp. 2, 25, 26, 27, 76)