if you mean there is not enough product then run a couple more cycles of pcr or 2 tubes of amplification. If it is a matter of enough dna but in too large a volume then you can column purify and elute in a lower volume as Mani sas, precipitate with ethanol/acetate and redissolve in a smaller volume, spin through a molecular weight filter that retains your dna or if your lab uses sephadex you can remove water by swelling a tiny amount of dry sephadex which will remove water and leave more concentrated dna in the excluded volume....there will be some loss of dna with this method but it is very quick

Why you meant "its too low concentration", PCR product mean it will have more copy, can be increased by increasing reaction volume.

Do you want to concentrate mean, go for direct PCR product purification, elute in minimal volume of E buffer (Use 20ul of E buffer instead of 60-100ul).

Bests

if you mean there is not enough product then run a couple more cycles of pcr or 2 tubes of amplification. If it is a matter of enough dna but in too large a volume then you can column purify and elute in a lower volume as Mani sas, precipitate with ethanol/acetate and redissolve in a smaller volume, spin through a molecular weight filter that retains your dna or if your lab uses sephadex you can remove water by swelling a tiny amount of dry sephadex which will remove water and leave more concentrated dna in the excluded volume....there will be some loss of dna with this method but it is very quick

Again perform PCR using your amplicon as template with forward and reverse primers you will get good concentration. If problem persist go up to 36 cycles. Don't trying to increase your cycles too much that leads to noise. increase reaction volume spin down and load in gel and run it and extract it from gel using kit.

It is hard to understand what exactly do you do, experimentally, but if you try to purify DNA from gel and then sequence it, make a big well, and load higher volume of PCR product to the well. But again, it is not clear what exactly you do

Increase a bit the template concentration and cycles.

Step 1: using high template as startup concentration and increased number of cycles. Step 2: use the low concentration of pcr product( if it's still low) and use that as template and then repeat the pcr with max cycles. That would yield a better/high cone traction product.

Also keep in mind the polymerase used. The half life of the enzyme would allow you to go only to a certain number of cycles.

If you want to increase the concentration of the reaction you have, you could column purify or better still purify using SPRI beads. This would give you will get a higher recovery  than columns and you can elute into a smaller volume thus increasing concentration. 

If its a matter of improving your PCR efficiency try more template (but remember never more than 10% of your overall volume) or perhaps try a gradient to see if your primers have a better annealing temp you could try. 

If your PCR product is simply too dilute and you have a reasonable large volume, and you have eluted in water after you have removed the remaining primers and nucleotides (when you have prepared your PCR product for sequencing), you may also concentrate the PCR product in a SpeedVac (or similar).  

You can make a new PCR product but your total volume can be 50 ul.. its enough for the sequencing 

If you have eluted PCR product in water, you may concentrate it in a SpeedVac (e.g. Savant, or something similar) .

Otherwise, you can repeat your final elution step in a lower volume of water.

Hope you are talking about microbial PCR product & Sanger sequencing!

Do you perform gel purification before sequencing or it is direct (like exosap purification)?

Do you perform Sanger sequencing in-house or it is out sourced?

Sanger sequencing until optimised - one could struggle. Once optimised we hardly have problems even without quantification of PCR product- before or after purification. 

I have out sourced as well as done Sanger sequencing myself. 

Set up more PCRs and use more template, then purify by columns or precipitate together. Both works fine ¡¡

1) I wonder how PCR product can be in low concentration. It is only possible if PCR reaction is not well optimized or you don't run enough PCR cycles. I suggest first to increase PCR cycles and if problem persists, re-optimize your PCR reaction.

2) If you cant do it anyway by employing option 1. run many PCR reactions (many tubes) and then gel purify. This method worked well with my students if quantity or quality of PCR product was a problem.

A: Agree with above comments.  You probably can either play with different PCR conditions or do several PCR reactions.   But, here is another way might be easier for you.  You can use Tini DNA/RNA column which was original designed for small amount of DNA fragments purification and concentration from agarose gel, but it works very well for any small amount of DNA or RNA concentration and isolation from trace amount starting materials.  The elution volume is only 5ul.  People are using this Tini column for circulating nucleic acid isolation (concentration) and you don't need to use RNA carrier and ethanol precipitation, just simply use binding buffer and wash buffer in any silica based mini prep kits.  Because these Tini columns are also silica based, just come with the smaller membrane.

Tini DNA spin column:

http://www.enzymax.net/columns/tini_spin_DNA_column.htm

you can increase the PCR cycles and DNA concentration in the PCR mixture. 

or you may need to re-optimize your PCR reaction. 

If you have such a low yield and you really have to do it, this is the way.

Let's say you have 50µl final volume PCR reaction.

- Add 5µl of NaAc 3M pH 5,2 (1:10 dilution)

- Add 110 µl of ice cold EtOH ( 2 volumes)

- Incubate for at least 1 hour at -20 ºC (ON incubation works better)

- Centrifuge max speed, for at least 10 min and if possible at low temperature. Remove supernatant.

- Wash your pellet with 200 µl 70% EtOH

- Centrifuge again for 5 minutes. Remove supernatant.

-Let it dry at RT for at least half an hour.

-Resuspend in either water or TE buffer. The resuspention volume depends on how much you want to concentrate your sample, if you need for example 100 ng/µl for your sequecing and you have 70, in this example and with this protocol, I will resuspend in 25 µl.

In an ideal world, half the volume should give double the concentration, but biology is not an ideal world.

Cheers and I hope it helps.

You can do an ethanol precipitaion and concentrate it. But with it may contain your non-specific amplicons as well. So the accurate way of doing it will be to run the complete PCR reaction on a gel and elute out the fragment of interest. You have a lot of gel elution columns available in the market which result in a 1-10ug yield. Otherwise you can go for the conventional phenol chloroform method (For which I suggest that you have a good amont of PCR product by either increasing the reaction mixture or keeping duplicate reactions). 

Are you talking about DNA directly extracted from biological liquids/materials or PCR products? Then after amplification, run a gel extraction (purification of PCR products).

The gel extraction protocol is designed to extract and purify DNA of 70 bp to 10 kb from standard or low-melting point agarose in TAE buffer. Up to 400 mg agarose can be processed per spin column. It usually works very well to prepare samples for DNA sequencing.

you can get your desire product by two methods -

1. you can run more PCR cycles to get more PCR product. So that, you can find your product in appropriate amount. after amplification, you should run your product on gel and then purify product by more efficient extraction kit.

2. this is alternative process and time taking process but more accurate. after extraction of amplified product; you can clone your it in any expression vector ex. PGEMT easy vector. and then transfer this ligated vector to particular bacterial strain. Grow these cloned bacterial stain and then isolate the cloned plasmid. you can find your product in proper amount in ligated form. you can use plasmid contained your desired product for sequencing directly. 

Another possibility is to make another PCR with products of the first PCR. You´ll get more of the original product in the second PCR. It is something like "nested" PCR.

nested PCR

Just rePCR your PCR product. or do the nested PCR.

I think Dr Zafar is right.

You may try the PCR purification kit and the speedvac.