The 1 - 3 - 6 Rule for IFR Flight Planning. predominant weather at your ETA through 1 hour after ETA must be equal to or greater than the military weather planning minimums for the approach you intend to fly at that destination.
Standard takeoff minima are one statute mile for aircraft having two engines or less and one-half statute mile for aircraft having more than two engines. Specified ceiling and visibility minima will allow visual avoidance of obstacles during the initial climb at the standard climb gradient.
If a usable precision approach is available: 600' ceilings AND 2 SM of visibility. If only a non-precision approach is useable: 800' AND 2 SM of visibility. If no instrument approaches are available: Descent from the MEA and landing must be conducted under basic VFR.
If there is any question of weather, you can (and should) retain your IFR clearance until on the ground and then cancel. However, there may be good reasons to cancel depending upon circumstances. For example somebody may be following you and cannot be cleared for the approach until you cancel your IFR clearance.
Definition: The 5/20 rule is a norm of the Indian Aviation Ministry under which national carriers are required to have five years of operational experience and a fleet of minimum 20 aircraft to fly overseas. This is applicable to all commercial aviation organisations flying passengers.