You decided to get instrument rating, congratulations. This will make you a better, safer and more confident pilot. You will need to make few decisions and hopefully this page will provide some guidance. Do not hesitate to contact me with any questions, I enjoy teaching instrument rating and will be glad to answer them.
What type of airplane should you use? If you are currently renting, but are seriously thinking about buying an airplane, buy it now and do your training in that airplane. If you plan to continue to rent, do you training in the airplane that you will be flying most often. To reduce cost, consider less expensive model with similar avionics, for example Cirrus SR20 instead of SR22 or Cessna 172 instead of 182, when both have G1000. You will learn the airplane and the avionics much better. This is particularly true for newer airplanes with modern avioncs such as Garmin G1000 or Cirrus Perspective. These two systems have common core and both offer wealth of functionality that you will learn how to use efficiently during your training.
Unlike for primary training, when simulators are of limited interest, for instrument rating they are very valuable. I use here the term simulator quite broadly, FAA has specific definitions of different classes of these devices. It ranges from desktop or tablet programs, that you can use to learn functions of buttons and knobs, to dedicated computers with very large screens, hardware imitating the actual knobs and buttons in the airplane. For example, Garmin has Windows desktop programs to simulate both G1000 and Cirrus Perspective, which cost less than $30 and don't require any additional hardware. They also offer iPad GTN650/750 app, which is free.
Make sure that you choose a flying club that has simulators and an instructor who is proficient in using them.
With modern avionics and autopilot, an airplane can fly itself from takeoff to 200 AGL at destination without you touching the yoke. We don't yet have an ability to land in 0/0 conditions (no visibility and indefinite ceiling), like airlines can with ILS cat III approaches and we still need to manage power, while larger airplanes have auto-throttles, nevertheless light airplanes come really close and sometimes exceed capabilities of transport category aircrafts.
Still, the very first thing that an instrument student learns is how to fly by hand using instruments as a sole reference. This involves proper instrument scan, proper trimming techniques and fine airplane control. Since looking out of the window doesn't help, pilotage and dead reckoning are not available and navigations using either VORs or more commonly GPS has to be mastered. Using these tools, we can safely fly houndreds of miles without any outside visibility.
Similarly as primary students spend disportionate amount of time on learning how to land, instrument students will be spending much time learning how to fly instrument approaches, to transition from enroute structure to landing. It is truly magical when a runway materializes itself at 200 feet AGL right in front of the airplane, but it is hard work to be able to manage it consistently. Approaches will be flown both by hand, using only raw data (basic radio signals) or using full automation and autopilot. The menu is impressive: traditional radio-based approaches including ILS, localizer, VOR or modern GPS approaches (LPV, LP, LNAV) together with holds, procedure turns or DME-arcs.
Maneuvering in the system, as IFR flight is often called, includes new phraseology for communicating with ATC, preparing flight plans, receiving clearances and managing flight in real time. Weather for an instrument pilot is a much more serious business and includes understanding how to avoid risks related to thunderstorms, when we cannot see them or icing in clouds, which can bring airplane down. Begining students often think that instrument rating is a license to fly in any weather, hopefully by the end of the training they will understand that isn't the case. As an example, in spite of having a turbocharged airplane and TKS ice protection, I do not fly over Sierra Mountains in IMC.
No aviation certificate or rating can be obtained without studing regulations and instrument rating is not an exception. Unlike for private pilot certificate, AIM (Airman Information Manual) is an often consulted reference, together with FARs. ADM (Aeronautical Decision Making) receives higher attention, since risks are higher, techniques and procedures to mitigate them are more important.