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Yes, turning the bike upside down is the best way to adjust the derailleur without a bike stand. It puts the derailleur closer to you and keeps both wheels and pedals free of the ground. The only situation where this method would be problematic is in strong winds with the potential to knock the bike over, but you can stand with the bike partially between your legs to catch it if it falls. 

You need to make adjustments _while_ the bike is pedaled. This is very difficult if you're using an extra hand to balance it on the kickstand.  Laying the bike on its side will cause one pedal to dig into the dirt, unless you try to balance it on something (generally precarious and may scratch your paint). 

If you have additional work to do on your bike and access to rope and a wooded area, you can also hang your bike so you don't strain your back leaning over it. This is, however, usually unnecessary for the time needed for a trail adjustment.