What are the best approaches for preparing to take the SIFT and getting letters of recommendation?

Experiences will vary on the LORs. I personally sought out a senior Warrant that was over 4 hours away from me (there was no aviators near me at the time). When I arrived for our meeting, in business casual attire I handed him a binder with my complete packet, other LOR’s, and accomplishments. We talked about my accomplishments and aspirations. He warned me how hard it was to be an aviator and how demanding the field can be for a Warrant. Nevertheless, he wrote me probably the best LOR I have ever received. If you show motivation, and desire it will go a long way! Good luck!

You can get a SIFT study book off of Amazon for $20 bucks. It definitely helps prepare you for the SIFT. As far as what to focus on, focus on whatever you're weak in. Personally I spent more time with math and mechanical comprehension.

As far as LOR's go, if you live reasonably close to a base with an Aviation unit, I'd make the drive down there and head straight over to the CAB. Warrants are everywhere and are more than happy to help you out. Generally you should seek out the LOR's when you've completed a majority of your flight packet as it shows you're serious about becoming an Aviator.

Honestly if you have a good understanding of math and english it’s not that bad, but some of the parts are kinda confusing. I took it with almost zero prep work and scored a 67. I would recommend if you buy a book to just time yourself doing the practice tests. The practice tests are harder than the real test, so they will definitely help you. I had access to one thanks to the Ed center, so you could ask them. The library on most posts has a copy, or can order one, of a sift practice book.
To answer your second question, just go talk to some people. I literally walked down to my local aviation unit and asked their staff duty if there were any flight warrants I could talk to. I got a name, sent him an email, and we had a nice sit down. Be prepared to answer questions like why they should support you and why you want to be an aviator. The CW5 that helped me was a great guy, I talked to many 4’s and 5’s and all of them gave me great guidance. Worst thing you can do is ask.
If you need any help just let me know!