Time from tissue collection to fixation should be as short as possible.
Volume of fixative has to be always 50x volume of sample. Use more fixative rather than less. Poorly fixed samples are unusable for sectioning and analysis.
Liver is quite sensitive to overfixation. To avoid tissue spalling during sectioning do not fixate liver in 4% formaldehyde longer than 24h.
For cryosections, it is better to fix the samples in 4% paraformaldehyde.
Long term storage in alcohol may harm some rare antigens and phosphoproteins; specificity and quality of an antibody recognizing such “difficult” protein should be properly tested prior to use.
High static electricity may cause sticking of the sections on the blade holder. To avoid this, wet the paraffin block with water. It will help for two next slices and then the blocks must be wetted again.
In situ hybridization could be also performed on paraffin embedded tissue samples. For this purpose, fixation overnight in buffered 4% formaldehyde is recommended.