First off, I would suggest trying to save chibis/bentos (40 chibis can be used to build one Bento ((ten of each character for orange or red Bento)) - you can also sell other items for chibis or bentos. OR if you have a pizza bikini, hypnocat, or moneydogs SAVE THEM. Then, you can go to an ec club where they only do the ec drop parties (Pizza Pop, Cat Cafe, Dog Star) which is going to give you more money for upgrades.
Save all your money for hiring tutors and for your dorm tower. In the dorm tower, only use dormmates that have the highest amount of strength or intelligence, not the ones that split it. You can decide whether you'd like a strength build (more strength than intelligence, which is more common) or an intelligence build (vice versa). You can also do an even build where your stats for strength and Intel are the same - which in my opinion is sometimes better while you're starting off.
I would suggest trying to save your items that have strength and Intel attached to it, and sell your avi shards or the furniture you don't use. Sometimes though it's hard to sell smaller items like that, so if you have to sell your stat items, do it. You can always get more or buy more later.
Overall, ec parties and tutors are some of the best way to make money. Good luck!