This is a hard subject to write about beyond offering some general observations and simple advice. Different regional factors including farming and crop differences, irrigation methods, topography, vegetation, grazing animals, wetlands, spring mud, winter snowfall, and other concerns all mean that local knowledge and experience are most helpful. What works in one area will be useless in another. Still, below are a few ideas that might be helpful to you.
Especially if they have been allowed to deteriorate to some overgrowth and/or uncontrolled edge vegetation, these private strips are not always preferable to landing in a good wide farm field. Here, your wingspan matters – as does the type of airplane or ultralight that flies (or maybe used to fly) out of that location (high-wing airplane pilots don’t care as much as you do about lateral obstacles). You will have more options for private airstrips in a 13 or 15-m glider than you do with a larger span machine. More than once I have flown in deteriorating conditions to a private strip that I discovered on arrival was unlandable. Once I was actually confronted with a big private wedding tent erected on the runway! So, you should scout for other fields and options on the way into such a private strip and be prepared to abandon the planned airstrip for something less dicey. A sense of the seasonal crop height can also be helpful here. A narrow strip surrounded by 10-inch corn in the springtime will be much less inviting months later when the corn is 5 feet or higher. On strips with some vegetation growing on the runway, try to avoid rolling over the growth – it can take out a landing gear door quite easily. Obviously, a narrow strip is an even greater challenge in a crosswind of any strength.
In New England where I learned to fly, there was an interesting airport hazard called “snow stakes”. These were 5-foot bamboo poles cable-tied to the runway lights to help winter snow plow drivers avoid plowing up the lights. There being no reason for the airport to remove them in the springtime, they became a perpetual landing hazard to gliders using those airports and often forced us into adjacent farm fields. Assuming that your narrow small airport doesn’t have these and has moderate-height runway lights, there is a technique of off-runway centerline landing that allows the fuselage of the glider to get quite close to the lights on one side (which is almost always lower than the glider wing root which passes over them) while the other wing tip easily clears the other set of runway lights. This method can be used to get a large wingspan glider into a narrow runway if there is no vegetation or obstructions outside the line of runway lights. Some small airports have a grass or dirt infield between a runway and a taxiway that can be tempting because it is wider than the runway. However, unless you are certain that these infields are landable, the paved runway is usually a better option. There can be chuckholes, drainage fixtures, or electrical boxes in the infield that you will not see from the air.
I generally prefer a cut or low crop field to an unimproved pasture for landing out. Usually, a pasture is rolling or has a side cut has rocks or chuck holes in it, and has grass of uncertain height. It may also be populated by grazing animals. A pasture that shows signs of recent mowing can be good (and probably does not have rocks) but be very cautious of a rollout that crosses from a mowed area to an unmowed area (or vice versa). Frequently the mowing line or border will be the location of a barbed wire fence – very dangerous and almost impossible to see from the air. See also the comments below about crossing roads into a pasture if there is a road nearby. Source: ‚Whingsandwheels, Roy Bourgeois‚.