Here you find some tips & tricks that are easy and inexpensive to implement. 

Audio analyzer: 

It seems like soundcards to PC's are becoming better and better, by using a soundcard and PC software you can easily build your own audio lab. 

A PC soundcard can be used to measure  the frequency response on an amplifier etc. A good soundcard (Turtle Beach) is good enough to measure a valve amplifiers frequency response. 
Calibrated microphones are expensive and hard to find but even a simple one can be used to roughly measure the frequency response on your loudspeakers. 

Function generator -Download your own function generator to be used with your PC soundcard. (70kB). 
Spectrum analyzer -A spectrum analyzer is also nice to have. (190kB). 

Phonoplugs: 

This is a tweak you maybe don't like if you have spent a fortune on German high-end connectors, remark though that the plugs shall fit the other equipment you have and they don't always do. 

There is no real standard for phono connectors, the size of the center pin is what differs most between different manufacturers. Hold the plug with a firm grip in your hand, push the center pin a bit sideways with your thumb (not much), now you will have a good connection between the plug and the chassis connector (at least on one side). You can twist the connectors sometimes to remove oxide on the side with less contact pressure. 

"Lack" table: 

This is and old tips which was common ten years ago (in Sweden), today not even the "Linn fanatics" use it, but I still think it is worth mentioning. 

IKEA's coffetable "LACK" can be used as a perfect rack for record or CD players and other audio gear. If you remove the bottom cover and the "cardboard filling" between the top and bottom cover you have a light "rack" top with stable "legs". The legs can be filled with sand if you want it to be really "advanced". A number of these Lack tables can be stacked to build a large rack, the legs can also be shorted if you need several shelves. The best with the whole thing is the price, you can still buy a Lack table for less money than one CD!! 

Striking surface (of a matchbox): 

This is another old tips very common ten years ago, today you can use special aluminum oxide paper instead of this but it may be hard to find. 

Ordinary striking surface (of a matchbox) can be used to remove dirt and oxide from pick-ups (unused striking surface without pattern). Dirt easily stick on the stylus and become harder when you play records. -Drag a couple of times back-to-front and you  will grind off the hard covering.