You can read Ways and Means online at the Perseus Project. Joseph Nicholas Jansen has an interesting dissertation on the work and its place in political economy.
Xenophon opens by noting that some leading politicians (prostatai) in Athens have claimed to be interested in justice, but have used the poverty of Athenians as an excuse to treat the allies of Athens unjustly. Thus, he says, he began to think about whether it might be possible to sustain Athens on its own land. This seems possible in terms of the usefulness of the land itself, which has a number of advantages: the climate is relatively mild and good for a variety of different kinds of plants, the land has a large quantity of good stone, and, of course, there is Attica's famous supply of silver. Athens is ideally located for trade, and far from any barbarians that could cause trouble.
In addition, Athens has a large population of metics, i.e., resident aliens, who both support themselves and pay taxes. Xenophon thus recommends that some study be devoted to reducing burdens on the metics where these burdens do not clearly benefit the city; the obligation of the metics to serve in the military forces of Athens should also be abolished, but they should be allowed, if they volunteer, to fill more than just infantry positions. As there is room in Athens for houses, a system should be developed to allow them to apply for freehold housing within the city walls, which the city can then use to draw in the best of them.
Of course, Athens is also a major commercial center already, with excellent ports and a good market. Making the city more efficient and hospitable for merchants would contribute to trade, and thus of trade-based revenue. Notably, it, like better treatment of the metics, would increase revenue without requiring much more than Athens already has and the will to put them into effect consistently.
Some revenue-raising projects themselves require capital, but Xenophon argues that it should be possible to raise this capital by borrowing from the citizens themselves. Citizens in Athens already contribute a great deal to build warships, despite never having any opportunity to receive a return on the investment; it should be possible to convince citizens to invest in a capital fund that will certainly provide such a return in interest, backed by the city itself, which is far more durable an institution than any other in which they might invest. You can also enroll such investors in a list of benefactors, which might even draw foreign investors for the prestige.
Out of this capital, one can build the infrastructure for simultaneously collecting revenue and encouraging trade (3.12-13):
When funds were sufficient, it would be a fine plan to build more lodging-houses for shipowners near the harbours, and convenient places of exchange for merchants, also hotels to accomodate visitors. Again, if houses and shops were put up both in the Peiraeus and in the city for retail traders, they would be an ornament to the state, and at the same time the source of a considerable revenue.
Xenophon also considers the possibility of using the capital fund to create a merchant navy -- ships owned by the city and leased out to merchants.
Section 4 brings us to the most extensive discussion of the work, on the subject of what should be done with Athens's silver mines. The silver mines require considerable labor to tap properly, and are also an immense resource, and therefore are an opportunity for more massive economic expansion than is found in other trades. Silver, in addition, is both a precious resource and a backup currency, which means that there is a continual demand for it. Thus he approves of the Athenian policy of allowing noncitizens to participate in mining. In practice, of course, the actual laborers in the mines are generally slaves, and Xenophon advocates that Athens build a slave labor force -- three slaves for every citizen -- to lease out to those who wish to try to make a profit from mining. In addition, he advocates a system in which both Athenian demes and private interests are able to share profits by cooperative work.
All of this, as with the previous suggestions, can be implemented gradually -- as he says, it doesn't matter how many houses, ships, or slaves we are talking about, since each one begins generating some revenue immediately. He also notes that these all generate second-order sources of revenues -- for instance, an expansion of mining increases the population in that area, which would create a need for a market and opportunities for new construction, both of which can be sources of revenue.
All of this is interesting, but it seems that Xenophon has a larger conclusion in mind than just to propose some practical policies. This becomes clear in Section 5:
If it seems clear that the state cannot obtain a full revenue from all sources unless she has peace, is it not worth while to set up a board of guardians of peace? Were such a board constituted, it would help to increase the popularity of the city and to make it more attractive and more densely thronged with visitors from all parts. If any are inclined to think that a lasting peace for our city will involve a loss of her power and glory and fame in Greece, they too, in my opinion, are out in their calculations. For I presume that those states are reckoned the happiest that enjoy the longest period of unbroken peace; and of all states Athens is by nature most suited to flourish in peace. For if the state is tranquil, what class of men will not need her?
Peace, then, enriches the city. Nor does political ascendancy come entirely by war, either; the Athenians did not achieve preeminence in the Persian Wars by making wars on other Greeks but by being useful to them. After this hegemony was lost, it was restored again, and this, too, was with the cooperation of other Greek cities that found that giving Athens power resulted in benefits for themselves. Moreover, if Athens really and truly worked to uphold peace among Greek cities, Athens's own safety would be in the interest of those cities; and if she were forced to defend herself, a record of peace would mean that nobody could accuse her of doing so for unjust cause.
Having laid out his case, Xenophon summarizes the benefits and prosperity that he thinks will flow from putting his proposals into effect, and, if Athens decides to implement them, he recommends that they start by asking Delphi and Dodona which gods should be propitiated so that the gods would look with favor on their undertakings.
* Poros is literally a way or path. The word seems in this context to be used to indicate a way to obtain revenue; the revenue itself is prosodos.
* Since the work seems clearly to refer to events in the aftermath of the Social War, when Athens had lost its hegemony for a second time, and to the beginning of the Third Sacred War, it is common to date the work 355/354 BC. This is tied to the book's emphasis on creating prosperity without imperial oppression.
* It's easy to focus on the economic policies, but it's worthwhile to step back and look at the whole. Doing so makes it clear that to a great degree Xenophon is really advocating a healthy operation of the city: it should be able to support itself but also exist in mutually beneficial relationships with allies, it should build up those things in the city that sustain it, it should encourage schemes and projects in which citizens working for their own benefit are also working for the benefit of the city, it should treat its resident population well, it should treat its allies well. The policies trace out major features of city life, and at each point advocate in some way that a gap be closed between private interest and public good.