One option is to look at one country that has set goals and published about their efforts to develop as a state. Kazakhstan is in an ongoing process of goal-setting and development. They have set goals in a variety of areas including financial, language policy, and education. Here is a description of their most recent goal-setting efforts: http://en.wikipedia.org/wiki/Kazakhstan_2050_Strategy.

i believe GDP per capita is a good indicator with a valuable database for a lot of countries

if you are querying the measure of developmental orientation of the state - then I would respond: The measure of 'developmentalism' residees in reactions and responses of the state to the needs and priorities of the most vulnerable segments of society following Sameul Bowles thesis on productivity-enhacing egalitarian interventions/programmes/projects  

I think your first question should be: what do I mean by development? Once you have that more precisely defined then you can work out the best way(s) to measure the degree to which it has been achieved. Other commentators here have mentioned GDP, productivity-enhancing egalitarianism, language policy, education ... to which one might add political stability, precise and respected borders, health, child mortality rates, etc. etc. All are measures of the broad development of a state, but none are a specific yardstick. If you can decide what you're looking for then it will be easier to know when you get there!

This is like saying everything and nothing! 'What do I mean by development?' is the eternal question ....to which I would retort: 'It is written that I should be loyal to the nightmare of my choice' (Joseph Conrad).  Please furnish your nightmare/dream

The development of a state (country) is a field or subdiscipline that emerged in the 1940s and has flourished afterwards. The literature and trends of the discourse have evolved by decades afterwards with specific concepts/terms designated to describe emphasis/focal points by those respective decades. Read widely, voraciously, wildly,. Keep identifying these patterns, agreements, new concepts, as they differ by economic regions and globally. Refer to Smith & Todaro's Economics for a developing world, and a whole wide array of journals. You shall not lack publications on this subject matter. Good luck

The word development supposed to measure the condition in starting point toward progress, BUT this word's meaning in our "mosaic system of belives" could carry more than only one meaning, even it could have two opposit meanings from two different views: one, could believe in a condition as a development, but the other one 's perspective it could be called "taken over by others" or, " being enforced to change ", for the very same situation. The social structure of any surrounding culture is the effective independent variable that gives different shades to this open Mosaic system of thought.   

If GDP is criticized, many scholars propose alternative indicators. And it is true there is very little consensus about what development is. As for me, I would suggest

https://www.researchgate.net/publication/227382695_L%27espace_de_libert_comme_mesure_synthtique_du_dveloppement_territorial_durable?ev=prf_pub

Article L'espace de liberté comme mesure synthétique du développemen...

One of the yardsticks of development is income per capita. This measure per se does  not lead to development. High income per capita does not mean that  the nation has achieved development as  the development concept is contingent to democratic institutions and sound policies.

If you want to measure a country's human development, you can look at the Human Development Index (HDI) - published yearly (I believe) by the United Nations Development Program (UNDP). It measures life expectancy, education, literacy rate and so forth. Alternatively, GDP per capita can also give you a idea of people's income, but I don't think it is as comprehensive as the HDI, as GDP per capita is simply the ratio of GDP over a population, and it has been criticized by many scholars. 

The popular notion of "globalization"  in recent decades has deeply downplayed the historic notion of "national economic development" and today countries are expected to just "integrate" into the global economy as they are, regardless of what level of economic development they've achieved. I think this is both dangerous and wrong. A clear focus on a national development strategy should supersede and then guide how a country integrates into the global economy. Until this time, and for hundreds of years before it, national development meant diversifying the economy away from a historic dependence on primary agricultural and extractives towards manufacturing and services as a way of creating wealth, higher wages, and a bigger tax base from which adequate public investments could be made in health, education, transport and social protection. But it has all been displaced by the globalization discourse. The last 15 years focus on the strictly social sectors of the UN Millennium Development Goals (MDGs) only furthered this neglect of the national development project.  I would say if you are still interested in national economic development, you should look at what all the rich countries did during the last few hundred years - manufacturing as a percent of GDP, manufacturing value-added as a percent of GDP, MVA as a percent of exports, and crucially, wages as a percent of GDP - if these aren't going up over time, then you're not really developing. Here below are a few tings I've published on this.

“The Myth of Africa’s Rise” in Foreign Policy (USA), January 4, 2013.

http://www.foreignpolicy.com/articles/2013/01/04/the_myth_of_africa_s_rise

“Getting Serious About Teaching Economics to Boost Developing Countries, Not Just the Big Guys,” Truthout.org, July 16, 2014.

http://www.truth-out.org/news/item/24825-getting-serious-about-teaching-economics-to-boost-developing-counties-not-just-the-big-guys

“Africa's Free Trade Hangover: Why African leaders have growing doubts about the virtues of free trade,” Foreign Policy (USA), August 7, 2014.

http://www.foreignpolicy.com/articles/2014/08/07/africas_free_trade_hangover

Would you accept "depends who you ask" as a complete answer?

There's money (GDP), welfare (e.g., MDGs or HDI) and more advanced notions of the level of development, including free media, transparent government, and a peaceful means for political transition vetted by the population through elections.

Please excuse my language, but you don't have to be a millionaire to realize that there's only so much eat-fuckable pleasure you can get before you reach a saturation of sorts, and much like Maslow, self actualization and the conditions which make it generally possible for everyone should be a pretty high goal. 

Basically, I think different things are relevant at different stages of development. Once everyone has enough food, measures of food poverty will not serve as much of a stimulus to make things better.  But if half the population isn't eating enough protein (whether animal or plant protein) then I would be less worried about average commute time in urban public transportation, for example.

Strong value system at all the systems-level of the state is the foremost. Institution-building, pluralism, constitutional -liberalism, good-governance, GDP growth, people's participation in the decision-making process at all levels, human resources development, egalitarianism, human-rights, separation-of-powers, devolution-of-powers, decentralization, and so on.

I have used a dozen indicators for assessing countries' success in my recent book (see below). Everyone of them tells a different story and together they tell the whole story.

Book Missing a Decent Living for Everyone: Success and Failure in...

In my opinion:

1. Welfare measured by HDI is quite telling (except perhaps for some outliers like oil-producing countries, which raises HDI through GDP pc without real developmental meaning for the common people).

2. Structural change, measured by the process of change of labour force activities, shifting from agriculture to industry.

3. Political liberties and personal security are as well desirable.

All depends, whether state institutions deliver, what they promise officially, given their constitutional/regulatory status, or not. 

There are several good work in this space that can be referred.

Some indicators - Longevity, Education, Health status, Poverty & Hunger and Income disparity & wealth distribution. Human Rights & individual liberties are equally important.