Cassette tapes do have a lot of hiss, compared to modern day digital audio.. Old home cassettes do degrade and in the worst scenario you will only get one go of playback.
Provided that your cassettes are mechanically OK (i.e. all the bits are in there, especially the one that presses the tape gently against the playhead), it's a case of cleaning the playhead, and adjusting it so it's aligned vertical/perpendicular to the tape/play-direction, or at least aligned with the head that recorded the material. A scary process if your tape is falling apart. Normally you shouldn't need to adjust this, but we're talking a time distance of 40 years...
Record in 24bit. Disengage all noise reduction on the deck, modern day plugins will beat it in 9 cases out of 10. Also turn off any EQ/Loudness. Focus on getting the best possible sound into the computer first.
Once you're past that point, look for EQ, multiband dynamic processors, a bit of gating.. even spectral noise reduction. There are professional tools on the market (RX !!) but they cost hard cash.