Conventional GM'ing wisdom is that if the player is not yet aware of the outcome of a dice roll, it should be rolled secretly, and not revealed yet. This comes up often with things like stealth and similar.
I've slowly come around to two other trains of thought when doing these, however.
1: Let the player roll anyway.
This may seem counter intuitive, but in many cases, I think it is acceptable to simply let the player roll now. In particular for thief characters, a highly skilled character can be argued to often have a pretty good sense of their surroundings.
If the thief fails a roll to hide in shadows, it can be interpreted as hiding without success, but it could just as well be applied as not finding a suitable hiding spot.
This has the benefit of driving the player to make another choice: Look for a different spot, find a different tactic, flee, prepare to fight and so forth.
Thieves often get treated somewhat harshly by the GM, especially when it comes to failed thief skills, and this can help soften that a bit, by making the thief class feel more competent and possibly realistic.
2: Let the player roll, later.
A favourite option of mine is to not actually make the roll until the result would become clear.
If the thief is sneaking into the castle, describe the sneaking action as you normally would.
When the moment comes that the ogre guard stomps over to the corner the thief is hiding in, to relieve himself, hand the player the percentile dice and ask them to roll at that moment.
The same can work for things like traps. For a bit of extra fun, give the roll to the player about to move through the trap that the thief attempted to disarm.
The methods above have a few benefits: They increase the players involvement in the game, can increase tension even for simple situations, and they reduce the amount of dice rolling the GM has to do (and more importantly, keep track of)
Give it some thought, and see how it goes.
There are two types of OSR players: People who like to invent their own games, and people who have a strong affinity for the "history" of the game.
If you are in the latter category, or just like old fashioned fantasy, you could do much much worse than giving "Three Hearts and Three Lions" a read.
It's one of the foundational stories that D&D was based on (In particular, you will find things like early references to law and chaos, many of the paladins abilities, the quest spell and famously, the D&D take on trolls here), as well as being a simple but very fun read.
It's not overly long or complicated, being essentially an adventure tale, so you can get through it in a few days, on lunch breaks or whatever.
And hey, if you do, you can help support the blog too. It's almost like charity except it probably won't make you a better person