With props, I always try to stick to the idea of organic prop placement. Use your judgment: anything that would be bolted down is probably safe to set at 90 degree angles, but anything else is safe to toss about. Barrels, crates, wood piles, mops and buckets... these are safe to put at odd angles and often more natural this way.
Repetition should be avoided, unless there is a good reason. The racks of tape prop you've used in that room is a great example: there are a few spytech rooms in some Valve maps that are viewed through a window where rows of desks and tape extend beyond sight, giving the impression of this expansive, possibly endless room! It's an amusing touch that fits in with the intentionally over-the-top spytech theme. In most other instances, repetition can come across as lazy or boring for the player. When you see a lot of the same prop in the same place in the same orientation, it suddenly begins to feel fake and can kill immersion.
I'm not going to pick on those racks because it's feasible that several racks can be lined up like that. However, the ceiling lamps are what I feel could use a change. In this instance you can probably get away with fewer of them.
Props are the easiest and quickest way to add complex detail to your map, but props alone cannot float the boat. Detail brushwork, texture variation and lighting are critical and just as important to pay attention to.
Sorry that my advice is all over the place. The others are right though: study Valve's maps and ask yourself why certain things feel right. Take screenshots of things you like and refer to them when designing. If you're making a spytech themed room, study their spytech rooms. You'll start to pick up on some common themes and techniques used to illustrate those themes.