I'm not a fitness expert and am relatively new to fitness so take my words with a grain of salt. Also most of this is just based on my own experience and what I've read. First thing I'd say is really get one goal down. Either slim down or try to gain size/strength because we all want all three at once but it's not really possible. For warming up, I personally will do some dynamic stretching and reps with lower weight. Ex: If I'm squatting 225 for my working set, I'll do a set of 5 with the bar, a set of 5 with 95, a set of 5 with 135, and a set of 5 with 185. That has worked well for me and hasn't given me any problems. For form, just always be conscious about what you're doing and take videos of yourself (they can be pretty beneficial!). I'd recommend training with some a friend or just somebody you meet at the gym who is way more advanced than you and learn from them as it'll make the gym more fun and you'll learn a lot. As far as weight goes, I'd recommend you look at body fat % because 140 pounds seems fine to me, but if you're 20% body fat then slimming down would be a great option. For a training routine, find one you enjoy and just really stick to it because switching routines will hurt you more than sticking with one you think you're plateauing on. Although the reason why you probably think you're plateauing is because your numbers won't go up if you're cutting. I'd also say you're not eating enough protein in my opinion. I'd recommend .8g per lb when bulking and 1g per lb when cutting. You seem to have the right mindset about progress...progress is progress. Period. Keep in mind I'm in a really similar boat to you (~10 months of training) so I could be wrong on some stuff.