'scuse the real basics here...but this may be useful to folks new to mechanicals...
1. ONLY use good quality tools. Cheap screwdrivers will be a bad fit in the slot and will ruin screws in no time.
2. Beware "Phillips" and "crosspoint" confusion. Phillips have a different blade point angle, and are identified by a small cross engraved between the driving slots (Union Jack style, if you see what I mean).
3. If you round out the slots of a crosspoint screw, first try honing a flat blade screwdriver, about 2/3 the width of the slot, into a chizel edge. This may bite into the screw and allow you to extract it.
4. If this fails, (carefully) drill off the screw head with a drill bit the same diameter as the screw shank. Then when you have separated the parts you can extract the screw shank using mini "mole grips".
5. NEVER put back a srew with a partly damaged slot - or next time you may have to resort to item 4.
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Cheers, Isetta