How to capture lightning through DSLR?

What are the basic requirements?
which is best filter to be used?

i'm using nikon.d7000 (18-105 mm) with UV filter

Depends on the time you're shooting (sunset, pitch-dark, etc)

For me, at 11:00 at night I used:
-
-
-

So @ ~f/5-5.6
~20 seconds
ISO 100

TRIPOD IS A MUST!

To get the shots, you use a tripod, a long shutter speed, and hope you don't get stuck!

Basic requirements;
- a tripod

Are you taking these shots at night? It will be easier as you can use longer exposures (which increases your chances of getting a strike in the frame) without over exposing. If you are trying to capture daytime lightning (during a storm) then some form of and filter might be needed to allow a longer exposure (it all depends on the light levels).

Set the camera up with the lens at wide angle (18mm in your case) and switch to manual focus - focus on infinity (this will stop the AF trying to hunt for focus in low light). Also have exposure in manual and set a smallish aperture (f11 or f16 if its brighter). Point the camera at ana area of sky where strikes are frequent.

If you have a remote release it's better as you can set the camera to 'bulb' mode and expose for various times manually.

If you don't have a release, then you can still do it - it's just requires more faffing about. Set the camera self timer delay to 2 secs and set the timer to give an exposure of between 5-30 secs (how long depends on ambient light and how many strikes you're getting).

No filter needed or recommended. Use a tripod and a long exposure and be prepared to "boogie" if the storm moves closer. You make a great lightning rod!