If you want to use big melee weapons, practice hanging back, then veering ahead far enough to hit your enemy with your weapon. Then, drift back. This makes the most of your weapons' superior reach and keeps you away from your opponents' faster weapons.
Concept art
Find the dead birds hidden in various locations to unlock concept art. Note: To find the birds easily, listen for the sound of flies. That sound indicates that a dead bird is near.
God Mode
You need to edit your savegames in order to be invulnerable, you also need a Hex Editor (Hex Workshop). Go into your install dir (default is: C:\Program Files\SEGA\Condemned - Criminal Origins) and click on "view the player data folder". After, go to Save/Profile000/SinglePlayer. Select the savegame on wich you want to be invincible and open it with a Hex Editor (Hex Workshop). Once it open locate this line (not very far from the beginning) DemoModeInvulnerable..0.000000 change it to DemoModeInvulnerable..1.000000 (as you can see you replace the first "0" by "1"). Save the file. Then you can load this savegame and you will be invincible.
Guns
As with all guns, it is best to save the revolver for fights against multiple enemies (or against exceptionally tough loners). Particularly weak enemies can be finished off with a combination of Taser and kicks instead.
Sprinting
Sprinting is not that useful on stairs. Save it for level surfaces.
Strategic dropping
Drop important weapons and tools near distinctive objects or in easy-to-find spots. By doing this, you will not have to search for them later.
Big melee weapons...