The correct way is to Compare the Minimums on plates for landing to the Forecast weather at your arrival for the Landing minimums. Whether or not the cloud cover and visibility forecast allows you to make the approach. When doing this you take into account what runways are available and if they have ILS or Other non precision approaches. This is because you might have a captain who is not qualified for a certain minimum. Take off Minimums are usually set unless the departure plate states that non standard minimums exist. In the US the rule for that one states all you need to take off is 1 statute mile down the runway if your in a twin engine aircraft. After take off you just shoot through the clouds. A take off alternate is considered if the ceiling and vis at time of departure do not allow you to turn around and see the runway under the clouds. In that case the T/O alternate is chosen must then be a particular distance from the Departure airport depending on the amount of engines the aircraft has. For example in the US the rule is with in 1 hour in still air with one engine inop for a twin engine aircraft. There is alot more to be said but i hope this helps.