I usually don't worry too much about needles and leaves on the slides. The "3 season" camping that we do means that, as a rule there aren't a great deal of falling leaves and needles to worry about. A few needles I don't worry about, the "squeegee" effect of the slide seals line the needles up along the edge and they don't cause a problem, usually any leaves that fall are brought down by the wind and they get blown off; again not a problem if there are a few leaves as they get get crushed when I pull the slide in.
That being said, we are on the road months at a time and I usually get up there once a week to brush the slide off and inspect the roof. I carry a Telesteps style ladder; 12.5 feet to allow full access to the roof:
Telesteps style ladder
It is part of my "Sunday" routine. Sunday is my "check the odd-ball stuff" day. I always do a cursory inspection of the TT daily, but, Sunday is the day that I actually get an air pressure gauge out and check the air pressure in all the tires (I've found that on my rig, they don't loose air much, usually < 1 lb. per week at most) and top up as necessary, check the LPG auto changeover status (unless we are using the Gas Campfire in a Can an awful lot, we get months and months out a 30 lb LPG tank, weekly checking of the changeover status is more than adequate to detect an empty tank and get it refilled) and get the ladder out and check the slide and roof for damage or repairs needed. The 12.5 foot reach allows for safely getting on the roof and the ladder stows easily in the back of the Jeep for storage. A 6 or 7 foot ladder would be a tad short for getting on the roof...