01) Outdoor shadows are awesome for sneaking
02) Contextual health is more awesome
03) Stat improvements are great
04) Flamethrowers and GEP guns are wasteful for the stealthy person
05) The crossbow is the second most useful weapon
06) The stealth pistol is the most valuable weapon you get
07) Lockpicks and Multitools are nice, but nothing beats the actual key/code/email and password
08) Stealth, health and environmentally effected modifications are more useful than any other mod
09) Every nook and cranny must be searched
10) Stock up on Candy bars/Soy Food/Booze early on, you'll never know when you need it
11) Throw away useless items like the crowbar, knife and binoculars, you'll never use them
12) Only use grenades in instances in which they have a profound use for the objective (i.e. Blowing shit up, not people)
13) Don't use the lockpick on that door with limited strength, see if you can break it with weapon you have, or some nearby TNT boxes. It's better to break a door, than open it.
14) Use every email you get, you never know when there is some important information in those open conversations
15) Read books and newspapers, not that it is useful, but it can give some backstory and understanding to the current situation
16) Talk to almost everyone. Future beneficial bonuses may come out of it
17) Stick to a baton/crowbar at the start, you can take down enemies without killing them wasting ammo, you will need ammo later
18) Aim dammit, don't just chew up entire clips because you don't want to wait
19) The non-lethal run can be accomplished with guns, just do little damage to the humans to the point where they run away from you in terror
20) Realistic is not kidding around, they will aim for your head
21) Throw away guns you don't use. If you don't use the assault gun, throw it away, you need the inventory space
22) Carry one type of alcohol
23) Multiple saves, I cannot stress this enough, for each different area you go to, you must create new save slots. You'll see why
24) Quick saves are for in motion purposes, don't use rely only on them
25) Deus Ex is the greatest game ever made

I recently started playing Deus Ex again, well about a month and a half ago. I downloaded some mods, better textures, OpenGL and it looks pretty good for an old game. One of my favorites, story and gameplay still hold up. Check out my profile page and look at my banner. I made that with a screenshot from the game... Red Star.

Kudos for point 25!
Deus Ex was/is Awesome! ^^

You forgot to point out that the swimming skill is useless...I figured that one out the hard way after heavily investing in it and creating a completely unbalanced and unplayable character...