Knackers
Fairly broad question which could take pages to explain depending on the type of acft you fly or your experience level however following may help clarify some points (certainly not gospel)
1) Planning a flight above the freezing level with forecast cloud at your planned altitude is asking for trouble. However if the cloud base was such that flight in clear was possible above the freezing level then things are fairly safe provided your climb and descent is not going to put you in it. Flying at night above the freezing level can be hazadous with unseen cloud. It can take a while however if you have picked up some ice on the climb thru the cloud to clear air for it to melt off especially in very cold climates. Certain controls such as trimming devices can become stuck.
2) If you dont have an instrument rating then you should not be anywhere near the cloud in the first place.
3) You will "generally" not get icing if it is a clear and you flying above the freezing level. A clear cold winters day for example.
4) It should be worth noting that just because you have an outside temperature above freezing doesn't mean you wont get icing. ie. High humidity can lead to icing in some engine components (carburettors) under certain conditions.
Again without ascertaining your level of experience its hard to answer fully, hope the points have helped. HOPEFULLY I wont be shot down in flames!