I'll just copy and paste my old post right here:
First, you'd want your screenshots to look good and be easily manipulated. So, go to settings and set everything to max in the Display settings or as high as possible. You should set the settings so the FPS is around half of a playable amount at the very least, otherwise it gets quite annoying.
Second, if you want to, set Pause to Caps Lock and Screenshot to G or something similar. Makes it easier. You can do this in the "Input" tab in the Settings.
When in-game, remember to press Tab and type in "Togglescreenshotmode" without the quotes to remove all unnecessary stuff from the screen. (HUD, crosshair, team members' names floating over their head, etc.)
Now you can choose between several things (I only have 3 different ways of making screenshots posted, but expect more in the future):
A. (easiest and least time-consuming). This is what I've used for just about every shot I've taken.
You should use the Bot Roster, or set the specify bot number to 0 and add bots in-game. Make sure they're Godlike. Add any necessary mutators and pick a nice map. Then add bots if you didn't use the roster by typing Addbots # . You can decide whether or not to spam the map up. If you do though, don't over-do it, or screenshots won't be as nice. Now, bring down console, type in God and Ghost and hide in a wall/roof/floor. Type Slomo 100 in console and wait a few seconds. Then type in Slomo 1 and Freezeall. Now walk around using FOV 120-130 by typing Fov # in the console, so everything's visible. If there's nothing spectacular to take a screenshot of, hide in the wall again and repeat the Slomo process. Make sure you turn off Freezeall first and re-apply it after Slomo-ing. When you find a nice scene, you should position yourself somewhere so the screenshot looks like you want it, then change the FOV to anything that looks good. Spend a lot of time with the position. I suggest that you find something that looks good, take a few pictures while tweaking your position/fov a little bit, then look for another good perspective. Make sure it's zoomed up a bit, but not so much that you can't see what's going on. Now, set slomo 0.05 - 0.2 and tweak your position until it's just right. Take a screenshot. Done! Repeat!
B. (A bit harder than the last, but not very time consuming)
Do the same as in A. except that this time, you only have one bot and it doesn't HAVE to be Godlike (although I prefer it that way). And instead of that Slomo 100 thing, you should use normal speed and lure the bot to wherever you want to take the screenshot. Now, here's where the hard part comes in. You should now try to align the bot with whatever you need. It will shoot at you, and stuff. This time, don't use Freezeall. Use Pause and Unpause until you've got a still-shot that is just perfect. It might help if you use a Slomo less than 1. Then, without unpausing, apply Freezeall. Now you can Unpause. Change your position, FOV and slomo as before and take the screenshot.
This is possible with several bots, but that is VERY hard to get right. The results will be splendifurous if you can do it right, though!
Also, you can shoot at the bot before clicking on Pause so it dodges or gets some cool effect to it.
C. (Not too hard, but might get quite frustrating. . .)
This is like the previous one. Use only one bot, but this time it might get easier with Novice bot. Now, what is this technique? You take pictures of death, that's what! You kill the bot and, like in the previous technique, Pause, put Slomo to something quite low and keep on Pausing and Unpausing until the bot's position is just right. Then, while Paused, use Freezeall and Unpause. Find the right position and stuff like earlier and take some screenshots. Now, you can try to do this with several bots and stuff, but, as per usual, this gets very hard. . .