Even though I may refer to EQ ing
(filtering really) the ends of the spectrum I think it is also important to think about the range of frequencies in between. I was recently teaching post audio for TV using Pro Tools and the students had to do a voice over read of themselves. After editing they were interested with the EQ stages that could be applied and the fact their own voices could be made to sound quite better than the flat original recording. Even though that was done with a quality mike and pre etc in a nice booth too. Inside a booth or tight space I have been known to mic close up as usual but also from a little distance away to get a different perspective on the voice over. This can help in post mixing when moving from space to space.
Each voice has its own character in its own way and it is good to be able to lock in on those frequencies. You can try creating a nice peak and sweep it slowly while the voice is playing back. This might help you locate the frequencies then you need to make a smoother boost curve and use less to just enhance etc.. It is hard to just recommend boosting or cutting at certain frequencies because they vary from voice to voice. It is good to home in on the characteristic sound of each voice which can involve a little boost in the right places to really bring these qualities out more.
If you are rolling off tops for outside uses then you can afford a little boost to keep clarity up there between say 4 and 6 K Hz etc.. I just want to convey the idea that after the correct filtering is applied then some EQ ing can take place for the better. Each character outside can have this EQ on its own track or buss making it all easier to control during post mixing.
Using effects is OK with outside visuals bit be mindful of where you might be. If you are standing between two buildings then some form of delay might be in order but if it's outside in a field with no reflective surfaces anywhere that won't work. That might just need the right EQ and perhaps a very tight convolution space to create a very soft sense of ambience even though it might not be there in real life. It's OK to take poetic license here and there.
The main thing is if you are outside have a look around and see where you are and get that nice stereo atmos effect in there to set it up perfectly. Every outside must have some sort of atmos and you will immediately get a sense you are out there. On shoots I have recorded atmos on serious stereo devices as well as the devices
Mike suggests. They are very good now and no one needs to know you are necessarily recording either. They can do that now easily. But if you are doing an animation for example you have to source the effects but they are all there and been done well too. You may need several effects to create the perfect atmos you are trying to create. For example a country fair atmos may be hard to source but all the individual elements are easily available so you can build it up. That is fun and you have control over the effects then on the timeline. World war 2 scenes may be harder to find but all the elements are very available making it easy to build an amazing sound atmos scene. Many mono effects too can be panned and treated for stereo effect later. When the atmos is wider the dialogue sits well right in the centre and does not fight the atmos anywhere near as much. Atmos can often benefit from a little EQ itself and compression to keep it under control and then finally automated for best effect.