Remember to sell all the items you don't want. A free space is much more valuable than some useless item.

As soon as you can, upgrade your hacking. You will need it to get into all of the rooms, and those locked ones often contain some good items.

Visit the shops regularly to find out what upgrades are available. They can be a life-saver sometimes.

You can observe the colors instead of reading all of the item stats. For example, the blue items are those you can find everywhere, while the red ones are rare and possibly valuable.

Work towards earning badges, as they can give you various rewards and special items.