Weight lifting/resistance training routine

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Hello!

I feel a plateau coming on. While at the beginning of my journey, I was steadily losing 1 lb or more a week, the last few weeks have been significantly lower than that -- about a half a pound or less. While I realize this isn't a "plateau" exactly, I'd really like to avoid hitting one at all if I can. Therefore, I've decided that I'm going to start lifting weights and such to help reduce inches and combat getting stuck in a slump. However, I don't have the first clue about what to do to kick-start my weight lifting. I do have a membership to a gym that has an extensive amount of equipment available, and I usually go 4-6 times weekly, but I've currently only done cardio.

I don't know that it matters at all, but I am 5'6.5" (yes, that extra half an inch is important to me!) and I weigh 135.8. I'd love to get down to 120, which is where I was a few years ago. I also recently (as in yesterday) got a fitbit and am hoping it give me the extra motivation I need to get out of my seat and moving some more.

So here are some specific questions that maybe some of you can help answer:

-- What are specific areas that I should target with my weight lifting?
-- How many times a week should I lift weights?
-- How do you vary your routine (from working legs one day to arms the next, etc.)
-- Any other tips/advice you can give me is great.

Any tips and advice you have is appreciated!

Thanks!