Creating your own instrumentation that is useful and of course accurate is a challenge, however it can be done and one interesting example is by Raivis Strogonovs who needed to weigh some LEGO bricks. Raivis solved the problem by creating a strain gauge based around a Wheatstone bridge circuit and some external op-amp circuitry that was mounted nicely on a custom protoshield. As well as the instructions you're also presented with the theory behind the project, which makes for an educational read as well.
If you'd like to learn about Arduino - but not sure how to start - then the best way to learn is with our Experimenter's Kit for Arduino:
The package includes a wide variety of parts, sensors and modules including: a servo motor, lights, buttons, switches, sound, sensors, breadboard, wires and more. Furthermore a Freetronics Eleven Arduino-compatible board is included to make this an extensive hobby experimenter, inventor and starter kit. However we don't leave you alone to figure it all out, included is a great project and instruction booklet, plus access to a supporting web page and software examples. In other words - this is everything you need to get started for a fun range of electronics and Arduino related projects!
So to get started or for more information and to order, check out the product page.