I just finished 1999 and got 1000 yesterday and honestly...it wasn't all that hard. Do as what others say about taking it slow and wisely choosing upgrades for your play style and you should be fine.
Personally I suggest you check every garbage can, scavenge every corpse etc... I also found it particularly easy if you upgrade Shields and Salts fully, along with fully upgraded sniper and shotgun. Using charge and posession and upgrading those both also is a HUGE advantage to tougher enemies like Siren and combat deck.