Well, everywhere there are rocks, anyway… :-)
So it sounds like you are in a fairly warm place with mainly herbaceous vegetation rather than trees. In Britain you would concentrate on south-facing edges that catch the sun, but in warmer climates insects are less likely to need to bask. Sweeping a butterfly net through the vegetation will pick up hundreds of small beetles, flies and bugs that you might not have seen just by looking. Get down on your hands and knees and scrutinise patches of bare ground. There will probably be carabid beetles running about and slower cryptically-coloured insects. Pitfall traps will also catch these but take precautions not to kill small vertebrates in them. Edges of water are likely to be very rich, especially if water is scarce. The shrimp juice method mentioned above sounds a good one. If nectar-bearing flowers are scarce, stick a bunch of garden flowers in a jar and sit and see what comes to them. Examine leaves for larval mines of flies and micro-moths. Try putting ripe seed heads in a jar and watch what emerges over the next month or two, a good way of getting flies and weevils. Keep it to one species of seed head per jar so that you know what species of plant the insects come from - useful ecological information and it may help with identification of the insects. That should be enough to keep you busy for one afternoon.
Insects love dry weather. Go out on a hot dry day in summer and reap a harvest.
That reminded me of another place I’ve observed invertebrates (not necessarily insects). Here we bag fallen leaves and old garden plants in large paper bags. These get picked up and composted by the city. We had a half full bag sitting by the garage door on a paved area and when we had to move the bag, all kinds of critters would scuttle around looking for new cover. You have to be quick!
But it might work to deliberately create this environment with a paper grocery bag full with some dirt. Let it set there for a few days then check to see what is under it.
I love this discussion because I think half the fun of observing is finding new places to observe. Not new parks or something. But new ‘nooks’ in the environment.
@rose I hope you come back to this thread in the future and give us an update on things you tried and what was or was not successful for your location.
Also
Starting a survey now and keeping up with it as your reforesting efforts proceed could provide some really useful data.
I haven’t tried it myself yet, but especially mercury vapor lamps with 160W to 220W in front of a white linen bed sheet at night near the edge of a forest should attract something.
Short answer: Move to a tropical rain forest. :D
Long Answer: You’ll find more insects by looking in more habitat under more varied conditions. In the replies above, there are already many good suggestions, but if you look only at flowers or only underneath stones, you’ll of course find less species than if you’re looking at flowers and underneath stones.
Usually, habitat and weather are also somewhat linked. For example: If you go to a patch of exposed clay in dry weather, you may find lots of ground-dwelling bees and wasps, but if it’s raining then they won’t be there.
At the same time, you might have greater success looking underneath rocks when it’s damp rather than when everything is dry.
Someone also already mentioned looking underneath leaves. The same principle applies here. Looking underneath the leaves of as many different plants as possible will give you the most insects (Especially for groups which are tightly linked to the host plant (aphids, gall-insects, leaf-miners, etc.).
I find it hard to generalise where exactly you’ll find the most insects. I’ve looked in places that should have been ideal, but found only a few flies, and I’ve looked in places which surprised me with their diversity. Going to a new place every time (even if it’s just a couple of meters from a place you already looked) is IMO the best strategy, and you’ll quickly learn what and how much lives where. :)
I forgot to mention earlier, there are lots of aquatic insect larvae that live in the uppermost layer of soil in river channels. I participated in an insect survey for an ecology class where we essentially just stirred up the bottom of a streambed and caught everything that shook loose in a fine mesh sheet. We rinsed the sheets into buckets afterward to concentrate everything we caught. This is somewhat disruptive to the streambed environment, so I wouldn’t do this in many spots in the same area, but it is a good way to find out what is lurking beneath the streambed.
You may also observe the variation in species based on the food available in different parts of the channel. Far upstream near the source where the water runs fast and had very little organic matter built up in it, you’ll find shredders that live mostly off of detritus that falls into the water from above. Further downstream, the nutrient load is higher, so you get algae growth and grazers that feed on the algae. At the terminal end where the water is slower, you get more sedimentation and filter feeders. And of course you’ll have a range of predatory species throughout.
Some of my best observations came from just being quiet. Go somewhere, and just sit. Sit, look, be alert for movement. Look at tips of leaves - they’re often used as perches. Peer underneath leaves, look for irregularities that might be something camouflaged.
Another nice dodge is to buy an inexpensive UV flashlight, and shine it on a white sheet at night. So many insects will come to UV light! Or just try under a regular light, like one over a door.
Looking near flowering plants in the daytime and light sources at night is a pretty reliable strategy.
If you live in a city, finding bugs can be pretty hard. I’d recommend growing a few potted plants to attract bugs to your area. It’s what I do, and it seems to have worked pretty well. But I live in india, where there are tons of trees even in the worst of cities. So it might be different where you live.