IMC for VFR Pilots
When VFR only pilots continue flight into instrument meteorological conditions the usual results are spatial disorientation of the pilot and loss of control of the aircraft from which recovery is almost impossible. This is a serious hazard for pilots without a current instrument rating.
Non instrument rated pilots have only a few hours of training under the hood in their logbooks, usually enough to qualify for their PPL or CPL license but in most cases that experience was obtained was years ago. Relying on that can be deadly within minutes of entering IMC conditions.
Low ceilings and reduced visibilities kill more pilots than thunderstorms, icing and turbulence (source: AOPA). This is due to the low experience level in IMC by VFR only pilots. Without visual clues in IMC, these pilots begin to rely on body motion and gravity sensors. The result is a confusing strugle between believing the instruments and what the body is telling the pilot (seat of the pants). With a deadly outcoming, usually.
Loss of Control Factors
When obtaining a weather report pay attention to cloudbases, temperature, wind and relative humidity (or dewpoint) this will give you an idea where visibility might be reduced.
Flying in IMC during the winter season or above freezing levels could mean aircraft icing. You will need an aircraft with de- or anti-icing equipment for known icing conditions. Wing profiles (lift) will be disturbed by ice and stall speeds and aircraft weight will increase.
VFR flight is usually allowed with visibilities down to one statute mile (1,5 km). But you as the PIC has to decide if its a wise decision to go on a cross country in these conditions especially if low ceilings are forecast. When a weather briefer reports VFR not recommended we can always take a look and file a pirep when conditions are better or worse. But pressing on in adverse conditions is just plain stupid.
With reduced visibility and flying near large bodies of water the natural horizon can almost become invisible. Continuing flight in such conditions maybe legal VFR but without good outside references VFR pilots will have difficulty maintaining correct aircraft attitude. The flight has literally become IFR.
Most aircraft have the familiar basic six instruments of a sophisticated EFIS needed for flying IFR. It is imperative to understand that VFR pilots flying such equipped aircraft use more external visual cues than they might realize. Because of that they may over estimate their skills in using these instruments after flying for many hours in VMC conditions.
Avoid flying in IMC conditions if you are not instrument rated and current. Divert to the nearest airport in VMC and remain clear from clouds.
Most countries do not allow homebuilt experimental aircraft to fly IFR or under IMC conditions unless strict rules were obeyed and inspections performed when these aircraft were under construction.
IMC Aircraft control
Should you inadvertently find yourself in almost IMC conditions then keeping your aircraft under control is very important. For this you will need to trim the aircraft straight and level at its cruise speed and power. This makes sure that you can control the aircraft with minimum effort (fingertips) and it will remain stable in pitch, roll and yaw.
Resist over controlling the aircraft and make all movements positively smooth, small and slow. If the aircraft has an autopilot then use its wing leveler function, so you can concentrate on navigation and communication.
Control altitude with power changes and use no more pitch change than one bar on the attitude indicator. Any turns should be shallow, 10 degrees bank or less, so that altitude loss is minimized.
Try not to combine maneuvers: descend or climb first then turn the aircraft. The pressure the pilot is under is more than stress enough even without complex maneuvers which would raise the risk factor enormously.
Remember: Aviate, Navigate and Communicate. Easy, first of all: keep the aircraft flying in the direction you need to go and then talk to ATC when you need assistance in these conditions.