What should i use my science on?

[BoggyDG]

Well, after following the tips dear ksp players told me in the "what do i do after mun landing?", i went to get an orbit to Minmus. Bit of a hassle getting the intersect, but i managed it. Now, after coming back safely(with 1400 delta-v before entering atmo), i got myself to 700 science!, Now, that is a lot for me, and i don't know what to spend it on. I've went for science tech part to get new stuff there, but still haven't got the gravity measurement thingy. All of my available upgrades are between 90-550 science in cost(550 being the rocket engines, and 90 being propulsion). I haven't gone as deep to ssto tech as much as science, and not much either to electricity(got only the first available solar panels). Now, what to go for next? is it the ultra-nuclear-radioactive-highlyoverheating^TM  engine? Or some science tech?

[KocLobster]

It's all about personal preference really, it's kind of up to you to decide what your prefer. I definitely recommend getting more science experiments early on to make it that much easier to gain science. Also, it helps when you start doing biome hops by not having to go back later to get those newly unlocked experiments you didn't have when you visited that biome earlier. Again, it has a lot to do with preference. That early on I also definitely prioritize the fuel systems tech node that gives you the external fuel duct, and better/more powerful rockets.

I also avoid the spaceplane tech nodes that are for planes; generally I don't bother with that until much later.

[Plusck]

Agree with the "personal preference" thing.

That said... definitely science experiments (as @KocLobster said, it avoids having to redo the same biomes too often, plus you always end up missing some and it becomes a chore to go back if you need just a few more points for that next must-have unlock.

In the 90s, definitely first barometer, then OX-STAT and OKTO, then a choice between fuel lines+T800 tank or the whole "control" package (RCS, torque wheel and the massively useful 1-Kerbal lander can) or the 2.5m engine package (Poodle and Skipper). Personally, I hardly use any other of the "big" engines other than those two.

And in the 160s - difficult to say. I'd probably go Electrics (all those solar panels) then Specialized Construction (docking ports, particularly) or Precision Engineering (HECS probe core for convenience, and the two small octagonal struts which open up lots of construction possibilities) then Command Modules (the Mk1-2 command pod is very heavy, but oh-so-useful and tough - and its sheer weight makes rockets fly better on their way to orbit!).

But really at this stage it is very much a question of preferences. And when you get up to the 550s, then yes the "Advanced Science Tech" with Gravioli detector and drills and ISRU is a game-changer.

[Hodari]

In general, I'd say your priorities should be:

1.  Any parts needed to solve problems you're already running into.  If, for example, you're constantly having issues with running out of power, get better batteries and solar panels

2.  Any parts you will need to complete contracts you have already accepted or to complete other missions you have planned in the very near future.

3.  More science experiments!  Spend some science points, get new experiments, use those to earn back all the points you spent and then some. 

4.  Whatever parts you need in order to progress on to further destinations.  Reaching more distant targets also means more more places to do science,

5.  Whatever other long-term goals you might have.

Early on in the game(At least up until you can reach the Mun and/or Minmus), number 3 and 4 should probably be even higher priority, but once you are able to land on the moons, you can enough science just from them to unlock everything else if you have to, so it becomes more a question of what is the most efficient way to do things.  In the very early stages though, you have to be at least somewhat careful with how you spend your points or you could end up not having enough points left to get what you need to progress further, but no real way to get any more science easily since you have so few biomes available to work with.

[Reaper_Works]

Pick planes or rockets and get those parts

[wumpus]

I'm not sure you can make it to Mun and Minmus without electrics (probes [but not mk1 capsules] die on a Huhann transfer to Mun, but you *could* go a lot faster).  Electrics make things easier, and let you bring Bob (for science resets) and still have SAS.

After that, unlock all the science instruments.  Not so sure the gravioli is within reach (I think the gravity detector is something else.  If not, I have a lot more experiments to do).  Grab everything else (you should have mystery goo, themometer, materials bay, baromater, gravity detector).

Nuclear rockets are the thing to get you to Duna.  Mobile Processing Lab is the thing to get you all the rest of the science (some say that nukes are the thing to get the MPL to Minmus).  WARNING: having a MPL in orbit around Minmus may make you want to do an unhealthy grind of science around Minmus, you have been warned.

I'm a big fan of the "rocketry" options, the heavier the better.  Mostly this depends on liking bigger rockets and SRBs (although mainsail is well into that chain, which eventually is a "must get").  But plenty of people like getting into space in other ways.