Hey, Just wondering if people had there own techniques for leveling up in Fallout3? I'm mainly asking for some advice. I've finished the main quest without doing much exploring as most of my searching the Capital Wasteland started with Broken steel and I've only just made level 14. Is this well below par for a character who has completed the main story quest and is just starting to do the main quests on broken steel?

Seems to be a little below what most people would be at that point in the game. I didn't personally finish the main quest until I did basically every single other side-quest. I was level 20 hours-before finishing the game. But I don't have any specific tips for leveling, besides just doing a bunch of side-quests. They are mostly pretty fun, so there's no reason not to just go for 'em. If you haven't already, start with "Mora" in Megaton.

Other good places to grind are Evergreen Mills (nice surprise there, be sure to bring tons of ammo), and pretty  much anywhere in downtown DC.  Lots of Super Mutants there.  But Bannister and Evergreen Mills are the two best ones I can think of. 
 
@FunExplosions said:

 If you haven't already, start with "Mora" in Megaton. "  

I stopped the main quest at "Take It Back!", to explore the wasteland and all the DLCs, since I own the GOTY edition.
 
I'm at level 24 right now. "Mothership Zeta", "The Pitt" and "Operation: Anchorage" are completed. Entering "Point Lookout". Using the Hellfire power armor since I've found it. 50+ hours of gameplay.
 
Actually, I found that leveling up in Fallout 3 to be pretty easy, playing in normal. Completing side-quests tends to boost your XP with 300+ points each, and most of them are easy and brief. Also, traveling alone guarantees that you'll earn points from every enemy.

I just work my way through all the quests, it hasn't taken much thinking about to do.

Id say work your way through the quests but I found disarming the vast quantities of mines lieing around a great XP boost.
 
Other than that, walk out of Megaton. Turn what ever direction and run all day in that direction discovering everything on the way.

Im at lvl 15 just doing the DLC, haven't really started the story. Just do all the side quests and you should be fine.

-raise the difficulty (hence saving a bunch)
-harder lockpics and computers give you 50+ xp 
-do side quests (you can find out which most are by looking at the achievements)
 
so just wander the wastes killing and finding tresure.

I am playing on normal and have completed Anchorage and Zeta and half of the main quest and The Pitt and I just hit 17. 

You could use that perk that gives you 10% extra XP wherever XP is earned.

If you're on the PC, get some mods. I've been having fun with these:
 
Cube Experimental is pretty much my all time favorite quest mod. I think it took me about 8 hours to complete, and has a very Portal-ish feeling. Highly recommended. It starts out slow though, but keep at it until you're done with the Cube chambers. It get way better. I honestly prefer this mod to any of the quests in the main game.
 
Another one is A Quest For Heaven 1 and 2. Again, giant quest that takes you all over the Wasteland and beyond. Unfortunately, the guy who made it is not a native English speaker and the grammar is well... atrocious. If you're willing to live with that, then I highly recommend it. It does get insanely difficult at some point though, since you'll run into a ton of spawns (sometimes  20+), and I had to activate God mode to get through those parts. Part 3 is in development as far as I know.
 
Played through those mods, finished Megaton, and I'm level 23. I haven't even touched any of the DLC yet. Great way to experience new content. Also, look for mods made by Puce Moose on the Fallout 3 Nexus. The guy knows what he's doing.