If you are using liquid animal glue, make sure that it is fresh as most have a limited life and will cease to work properly if they are old. This also applies to PVA wood glue and adhesive type glues, so check their use by dates, as there is nothing worse than trying to clean off wood glue that has not cured properly.

Tip; Some wood glues do not have use by dates, so when you purchase them write that date on them, as most PVA wood glues and some adhesive style glues can be stored in a cool place for up to a year.

Most wood glues and adhesives are effective only on surfaces that are free from moisture, dust and grease. Unless the instructions with your adhesive specify special gap filling properties, the surfaces should also be reasonably smooth with good tight fitting joins or joints.

Make sure that you sand and finish off any areas that would prove too inaccessible after gluing. If there are any small holes or cracks in the wood, fill them at this stage. An appropriate filler can be made by mixing a PVA wood glue (mixing ratio is 1/16 -1 part PVA glue to 16 parts water) with some sawdust: if you use sawdust from the same wood, the finished joint will be barely noticeable. If you are using an adhesive and sawdust thin the adhesive with the appropriate thinning agent, which should be the same as the clean up agent on the manufactures instructions.

Always 'dry assemble' your work to begin with. Blow out dust from any inaccessible corners of the work, if you do not have an air supply a vacuum cleaner in reverse will do the job, and then fit the pieces together. Having made any necessary adjustments and re-cleaned the joints, mark each part to eliminate the possibility of getting things in the wrong order on final assembly. With your job in the dry assembly stage now is a good time to work out which clamp will go where and to sort out your clamping blocks. Clamping blocks are scrape piece of timber that fit between your clamp and the timber surface being clamped, as not to damage that surface. Sometimes blocks have to be cut to an angle or shape to allow the cramp to hold the join or joint straight and not slip off the timber, this is something you do not what to be doing when the wood glue has been applied and starting to set.

[edit] Mixing and Applying Adhesives

When making up a mixed wood glue (dry powder style) or adhesive, use a small flat piece of wood as this piece of wood can be use to apply the mixed glue to the job. Follow the manufacturer's instructions to the letter, taking particular care when water has to be added.

You can also use a small artist style brush to apply your wood glue or adhesive or apply it straight from the container. Again, you should follow the instructions carefully and make sure that each surface to be coated receives an even covering. Glue invariably shrinks as it dries causing stresses and strains that will weaken the joint unless the coat is even.

Once you have applied the wood glue assemble and clamp the wood as soon as possible, removing any excess glue immediately that is squeezed out of the joints. For more information read Wood Glue-Avoiding Gluing Problems