See here:  http://www.reddit.com/r/buildapc/comments/1yg8xg/dos_donts_and_tips_for_first_time_bulders/


**Buying Tips:**  

* Plan ahead so there aren't future headaches. Make sure the parts will fit and that you have all the necessary cables.
* There's no such thing as 'future proofing'... I think a better phrase would be "future resistant". The order I would build a future resistant computer is this: PSU, Case, Storage. Everything else gets outdated fast.
* Microcenter is your best friend (especially for CPU's). Keep in mind Bestbuy or Staples might be able to pricematch Microcenter's prices. If you don't live by a microcenter there's Amazon, Newegg, and PCPartpicker.
*  You probably won't need a 1000W PSU, $300 mobo, or even SLI.
* Don't cheap out on PSU's. It can be the most important part in a build.   [Corsair, Seasonic, EVGA, XFX are notable brands.]
*  Don't buy a PSU with a 220/110V switch. It means it won't have Power Factor Correction too! If you do have one make sure it's set to 110V if you're in the USA.
* Buying a case too large for their needs. These days you can fit 6 HDD's into ITX cases. It depends on your needs though.
* Installing too many fans. A few large fans can move as much air as speedy, loud small ones.
* Slowly collecting parts. What if one of the parts that is sitting there idly is defective and the 30-day return / replacement is now obsolete?
* Don't buy a $500 single graphic card or run two cards in SLI and then only plan to use it on one small resolution monitor
* Don't buy a triple channel ram kit and pair it with a dual channel motherboard.
* An i7 is only necessary if you're utilizing programs that can take advantage of it's features. (Hyper-Threading, Multi-Cores, etc). If you're only gaming with no intention of utilizing those programs stick with the i5.
* Make sure the RAM/Motherboard (pins) are compatible as well as the CPU/Motherboard (socket). This information is usually found online or in the manual.
* Does your PSU have a 4 pin 12v connector for your CPU? Or 8 pin?
* Do not trust power supply calculators from manufacturer websites!
* If you're not going to play games or perform video/CUDA programming, on-board video is fine. The card will just create extra noise you don't want even when it's idle because it still generates heat that will cause other fans to spin faster.
* You don't need a 'k' series CPU, a Z Chipset, or an aftermarket cooler/heatsink(although this could make it quieter) if you're NOT overclocking. Alternatively you could use a Xeon if not overclocking.
* Buying an Optical Drive is usually not needed anymore. Everything can be done with a flash drive these days. Another option: External dvd drive.
* I personally suggest getting a SSD. They're amazing. Minimum 120GB. If not, get a 1TB HDD and grab an SSD later.
* Most people are perfectly fine with on-board audio these days. A DAC/AMP would serve you better than a soundcard anyways.
* Verify if your CPU heatsink needs a mount underneath the motherboard.
* Verify if your video card requires two separate power cables or not and that you have the correct cables coming from your PSU.
* If you have a case with front usb 3 ports make sure your motherboard has a usb 3.0 on-board header
* If you use an ssd or plan to add one, make sure your morherboard has a 6gbps sata port

**Building Tips:**

* Touch something metallic to ground yourself before you handle anything hardware related. You don't want any static buildup to discharge onto your fragile motherboard. When installing in the case, plug in the psu and leave the switch off to ground the case as well.  
* Put on the I/O panel before the motherboard.
* Screw in the "stand-offs" or mounts before installing the motherboard in the case.  (These prevent shorts aka fires!)
* Align the CPU, PSU, RAM, Cooler, and everything else the right way.
* Use about the size of a grain of rice for your thermal paste (or half a pea size) in the center of the CPU before applying the heatsink.  
* Read motherboard manual for front io connector help. (power,reset,hdd status, etc)
* Always put the SSD on a 6 Gb/s port, and always use the chipset-native ports (on the Intel or AMD controller) first. Don't use the marvel/aftermarket sata controllers unless you absolutely need to.
* Plan out your airflow before installing your fans into your case. Usually there's an exhaust on the back, and and an intake on the front.   Therefore, your CPU cooler should blow toward the back of the case.
* Build your PC out of the case before you build it in the case, and start with the minimum - mobo, 1 stick of ram, processor and GPU - then build it up from there. This will save you a ton of headache if one of your parts is defective. Most build it on top of the motherboard box or some insulating surface.
* Verify that your aftermarket CPU cooler will fit if you are using high-profile (tall) RAM.
* Most custom cases come with cable tie down mounts so use them!
* The CPU bracket needs a considerable amount of force to lock it in.   Lock in the processor before you put the heatsink on. Installing RAM needs some force as well to 'lock' it into place. It can only go one way!
* The CPU fan should always be a 4-pin header. Case fans can be either, but are often 3-pin. Fancier motherboards may have 4-pin case fan headers, but these are backwards compatible.
* Those tabs on the IO shield should not actually go inside any ports/jacks. They should also not be bent off as they act as grounding agents. The main one to look out for is the one near the LAN port.
* When removing a PCI-Express or SATA cable, be sure to disengage the card with the unlocking-mechanism
* Clean your CPU/Heatsink off with  high percentage ISOPROPHYL ALCOHOL before applying thermal paste


**Common Mistakes:**

* If you have 2 sticks of RAM and there's 4 slots, Check the motherboard manual as to where to put them.
* Throwing away the little plastic jumper piece on the mobo. It allows you to reset your BIOS.
* Interchanging +5V and -5V for frontal USB. Can fry a flash drive.
* Plugging in your monitor into the integrated display adapter (I/O port) if you have discrete graphics (a "graphic card")
* Mixing up the internal USB and 1394.
* Don't plug anything in while the computer is running!
* Buying 1.65V RAM, running it at 1.5V and wondering why you have instability issues.
* Not jumping into BIOS immediately after boot. (usually by tapping f12, or del)
* Touching the bottom of the processor or CPU socket.
* Not cleaning your your case. Dust is the main source of failure to electronics. It can short if you are negligent about it.
* Failing to realize some cases have a backplate for cable management as well as tie down mounts along the edges of the case.
* Not realizing the CPU has its OWN separate power cord from the PSU. This plugs into your motherboard.
* Failing to keep sensitive pieces inside anti-static bags instead of on top of them
* Forgetting thermal paste if not using a stock cpu fan.
* Failing to remove the plastic film stuck to the heatsink when mounting it to the CPU.
* Failing to get out a screw / part that fell into the case. It could short a hardware component.
* Failing to realize some video cards need power as well from the power supply.
* Failing to verify that all the fans are plugged in before powering on.

**Post-Building Tips:**

*  Don't forget to flip the switch of the PSU to "on" when finished building.
* Forgetting to use windows update after installing the OS.
* Get the latest drivers from the manufacturers website, not the disc in the box.
* Over-tightening screws when mounting your motherboard, heat sink, and so on.
* Not wiping your hard drive before an OS install. Don't think you can use your previous drivers on your new build unless you want to cross your fingers!
* Don't defrag a SSD.
* Set the SSD to AHCI in the BIOS.
* Make sure the monitor is on the right input
* Use Ninite to quickly reinstall common programs.
* If having hardware problems, update the bios. Reset the CMOS. Check each component and find the root cause.