Take a picture of every sample and document the general sampling area. It will make it a lot easier to locate the sample location again in case you want to return to collect more individuals of a particular species. In order to identifiy the sample on the picture, write the sample number clearly on the lid of the cup. Also, try to take the GPS coordiates of each sample or sample location.
A sand sample is a sample that collects sand in a small and clearly defined area. For such samples, it is useful to note the thickness of the oxygenated layer. We usually do not find macrostomids in evidently anoxic layers (often idicated by blackened sediment). Also avoid collecting black sediment in your sample, because it makes the samples go bad more quickly.
A 'Pete Sample' is a long, thin surface sample covering a gradient over different substrates or habitats (the name is in honour of Peter Ladurner, who 'invented' that type of sample). Pete samples are very useful in a 'range finding' process, for example, when you collect in a place for the first time. If you find some worms in such a sample, you can always go back and sample more accurately.
Several Pete samples can be combined into long transects, to start obtaining a better idea about the spatial structure of the specis distribution.
To sample in between vegetation, especially in fresh water habitats, a scoop sampling device can be very helpfull to collect and concentrate the material. This one was built by Gregor Schulte out of a discarded detergent container found on the beach, a 30 µm mesh and a lid of a urine cup. Basically, you need a sturdy funnel, ideally with a handle, and a fine mesh that holds back the animals, but lets through the water. The sampled material then collects in the bottom of the scoop in a detatchable cup. It's really an indispensable collection tool. Note that scoops can also be very successfully used on a flooded meadow. An alternative to a scoop is to collect vegetation, and to shake it focefully in a bucket of water. Both types of samples then are extracted using the bottle method (see Extraction).
These kinds of acrylic tubes are useful to take core samples in a more standardised way. However, many species tend to be quite superficial (at least species of the genus Macrostomum), and so taking deeper samples may not be so useful.