This depence on what spider are you looking for, but generaly their pop. densities are, as in predators, small, so you cannot excpet much more speciemns then 5. I have good results with cup-board traps, but also there are smaller densities. Or you can collect spiders during witer in their owerwintering nests - there are published cases of gregareous overwintering of Nort American species of Phidippus with some 10 specimens per nest. In Europe, there are known aggregation in landsnail shells (Szinetar et al., Hula et al., Bauchens, Bellmann) in case of Pellenes species. Or you can collect Philaeus chrysops, which is often overwintering in larger numbers betwen mainly limestone stones (stone lying on rock). eevrything depence on purpose for which you need these spiders - species etc.

On trees you could capture easy Salticidae by beating and by corrugated cardboard traps, but immatures are dominant.

Beating would be effective method to capture salticids, however until they are at a suitable height from ground. For the ones in grasses or foliage to the ground, sweeping net is helpful. I have used the kind of net (in image) for sweeping, which is usually used for collecting aquatic beetles. 

Hi, it certainly depends on the species and its microhabitat. However, generally sweep netting is very useful in more or less soft vegetation (grasses, annuals etc.). I use a V2A metal net frame, which is unfortunately heavy, but it may cut the grass before it gets broken itself. So, you get the right kick off effect and must not hesitate to get your net frame broken. However, this may be critical from a nature conservation viewpoint - it depends on the location.  Furthermore, spotting by sight on tree trunks, stones, molluscs shells etc. is a useful method. And, certainly, as already mentioned here, beating on shrubs, trees etc. Automatic traps may be stem-eclector (e.g. by Funke 1971; for example see here: http://www.ecotech-bonn.de/de/produkte/oekologie/baumstammeklektor.html) which can deliver good results for stem inhabiting salticids.  Pitfall traps etc. contain usually only a low proportion of salticids.

In addition to the methods described above, a D-vac (modified garden vacuum) can be a very efficient tool to collect spiders. This method enables you to catch spiders from almost all strata (from ground dwelling wolf spiders up to spiders walking on twigs). It is also one of the best methods to quantify spider densities by sampling a defined area.

See for example (http://onlinelibrary.wiley.com/doi/10.1111/j.1570-7458.2010.01094.x/full) for a critical discussion of suction sampling.

Although some companies offer D-vac's for arthropod sampling, it is relatively easy (and often cheaper) to modify a garden vacuum into a powerful tool for field ecologists.

In rocky and bare soil with little vegetation ecosystems, we captured a lot of Salticidae using pitfall traps. For soils that are difficult to dig, with exposed rock, we used trays with shallow (3 cm deep) as pitfall traps, covered with a protective cap higher than the trap itself and propylene glycol as a preservative.

Some years ago I did studies of small arthropod assemblages in salt marshes and on ocean beaches in New Jersey.  I used a sweep net like the one shown by Siddharth Kulkarni in the grasses, forbs, and low shrubs in the marshes and beach dunes, and pitfall traps like those mentioned by Jorge Mederos-Lopez on unvegetated sandy beaches.  Both methods caught Salticid spiders among a lot of other spiders and insects, but the numbers were relatively small in all cases, reflecting, I believe, the low densities of these spiders in those habitats, as Vladimir Hula suggests.  Just be prepared to pick your spiders out of a lot of other organisms that you will catch.

According to my experience beating method and visual search method is helpful for the collection of salticids. In visual search if we know about there retreats than we can easily catch. 

Butterfly nets maybe? But with some fabric inside. You can also use a white blanket, put it on the ground and catch with small pincers all the salticids you find.