The best way to improve the soil?

In the past I have always hauled some sort of manure but this year I decided not to for my veggie garden spot. I instead relied upon the mulch from last year to improve the soil and where I am not going to plant I am going to plant a cover crop of Berseem Clover. Is this also a good way to build up the soil or should I do both?

Both! It might also be a good idea to seed some dynamic accumulators that will bring up subsoil nutrients and minerals (daikon, turnip, etc) as well as some beneficial pollinator plants (asters, milkweed, etc). You can harvest some of the taproot plants but leave some in the ground to turn to soil and release those subsoil minerals.

MULCH super thick!

It's a great way to build the soil. Michael's recommendation of using multi species cover crops is also very good. So long as you maintain the moisture levels of your soil (not saturated, not too dry) and add organic matter it all works. If you look at the thread https://permies.com/t/57161/Photos-Joseph-Lofthouse-Garden On the third page there are some very good photos of the cover crop Joseph is growing this winter to rejuvenate one of his fields. I know he doesn't use any added fertilizers or manures and farms very successfully in a very harsh climate.

If you are careful of your source and have enough rainfall to wash away salt build up, then manures are ideal for the garden. Be careful of where you get the manures from, though. There are now persistent herbicides that frequently contaminate animal feeds. If you get manure from an animal eating these then you will be applying herbicide with the manure. They'll kill or weaken most garden vegetables.  

Organic should always be safe, and if you know the farmer you can ask questions. Many people who don't get certified organic still use responsible management techniques that don't spread these poisons. I buy pastured chicken eggs from a neighbor here and I can't imagine them wasting the time any money for organic certification. I still don't worry about accidental poisoning from them.

Another resource that is now commonly contaminated is straw. I don't know what else to watch. Many of the people here won't bring outside material onto their property because of these kinds of concerns.

Thanks for that reply. We get a lot of rain. On average we get over 50 inches per year. I am going with the cover crop because of the contamination from manure that you mentioned. I have not been so careful in the past but am trying to be a better steward now.

hau Bart,  Casie and Michael have given good methods.

I will add that when growing a cover crop it never hurts to use several different plant types in the same area, that way you get multiple benefits from one seeding.  
Don't forget spent coffee grounds,
they add nitrogen, some minerals and most importantly biological life forms (let the spent grounds sit until the molds and fungi spring forth).
I usually hold mine for up to a month in an old coffee container before spreading them, that will really help the roots take in nutrients.

Redhawk

Not knowing your exact situation, it's difficult to offer advice for the "best way" for your garden.

When I lived where there was sandy soil, hot summers, wet winters, I found that lots of compost and horse manure did a great job. During the summer months I used mulch, which was tilled in before planting a winter cover crop. I used winter rye, which was tilled in as soon as the ground thawed in the spring. It provided a lot of green/nitrogen.

I now live in the tropics and have learned to use lots and lots and lots of compost and chicken pen litter, plus use mulch year around. All my manure is homegrown in order to avoid herbicide contamination. Prior to having my own livestock, I collected horse and cattle manure locally from pastures that I knew were safe. I till in compost and the old mulch between each crop. I grow veggies year around, thus seldom plant a cover crop.

Thanks for the past 5 years I have hauled in chicken litter and will probably do so again next year I decided to let the soil rest. I have also rotated crops on plots in the garden and for the past 2 or 3 years I have brought in and mulched the garden in the summer. Before it was made into my garden spot it was a place to grass feed out cows before the advent of big ag feeding out places and then for the longest time it just returned to pasture and had leaves fall on it. I also plow in the leaves every year. The top soil is deep and it is more loamy than sandy. I have some poor soil I am going to rehabilitate to make a second smaller garden plot. It is very sandy but I am going to work on it starting this spring with cover crops and hauled in grass and leave clippings.