Generally speaking, for PVE I should look for these talents, taking into account the use case for each weapon:

• Destructive: increases Enemy Armor Damage by 15%
• Ferocious: increases Damage to Elites by 10%
• Predatory: heals on kills
• Responsive: Extra 10% damage at close ranges
• Prepared: Extra 15% damage at far ranges
• Elevated: Extra damage when over a car or anything higher (on M700)
• Skills based talents: competent, determined, talented, commanding

Unless there's specific needs, these are the preferred slots to put each weapon attribute from weapon mods:

• Muzzle: Headshot Damage / Critical Hit Chance and/or Critical Hit Damage (special case: Critical Hit Damage on SMGs that can't fit large suppressors)
• Underbarrel: stability, accuracy, reload speed or critical hit damage (special cases: optimal range on shotguns, accuracy for snipers, critical hit damage on SMGs)
• Magazine: always the Extended one (except when you know of a special case)
• Optics: Headshot / critical hit chance and/or critical hit damage (special cases: critical hit damage on SMGs that can't fit large scopes, accuracy on shotguns)

Source: 1.8 Guide.