Hello there! So I have this idea of getting a pet lo lvl 50, I was wondering if there ae any tips. I know there are some items to help them but they are quite expensive and I believe they are more useful at the end of the training. 

For example, do pets gain more experience fighthing against wild monsters or other beastlord's pets? 

Exploring is by far more beneficial than battling other players' pets. Islands offer an opportunity to defeat 5+ monsters for just 2 energy points, whereas a Beastlord's beast (1energy point each) only grants as much experience as one regular Explore monster (IIRC).

So when I spend those 2 points on exploring, I may gain approx. six monsters' worth of experience. If I spend them on "PvP" fights, I may gain two at maximum. Hope that made at least some sense. XD; The Arena seems to be designed to test your pet's strength against non-automated opponents rather than for exp boosts.

My own lvl 50 pet was exclusively island-trained. =)

When exploring, I like to explore the island as much as I can without engaging any of hte monsters. Then I start battling the regular monsters starting from the lowest level monster (hover your mouse over the monster to identify the level) and work my way up. I explore each newly revealed area as I go. Once the regular monsters are done I fight the guardian monsters (The red beast and the pink vine thing), again from lowest level to highest level. If I am still alive after defeating the guardians and I have a boss monster (the statues) I attack the statue, although so far its defeated me every time

@DragonSage, that's what I've always done as well, it's a great strategy - always makes the best of exploring. Personally I don't differentiate between guardians and 'normals', though; I just sort them all by level.

I have really bad luck on guardians regardless of level.  They almost always kick my furry/feathery/scaled tail.

I'll fight a higher level normal monster than a guardian.

Viriagan the reason I hit the normals before the guardians is I'm frequently able to defeat normals that are three or four levels above my pet's level but a guardian that is the same level as my pet usually wins

I do the same as Dragon Sage, xcept I battle lower level monsters as soon as I see them. Depending on pet I may battle same level monsters straight away as well.

For guardians, my general rule is "add three levels" to get a general idea of it's strength.

Also my only pets who can reliably defeat them have good genes, no red stats and at least one green or other nice gene like gracefulness. Even my best pets will still loose to mobs at the maximum level cap for the pets level sometimes.

Generally, for each pet, get an idea for what they can take on. Better genes make better fighters, worse genes mean you will have to stick closer to and below their level.
You don't have to go around everyone and wait until last, just watch their levels and avoid ones outside their "comfort zone" until last, and I always leave the guardians until last. I'll also tackle stragglers in order of level, unless the map is huge, awkward, and I just don't care.

Also, if I ever spot a magic shop or the building that gives experience, I'll go straight for it and avoid fights until I've used it. Same for the lab and pets with unresearched genes.

Build the sanctuary and ridinghall as soon as you can, and upgrade the ridinghall. Especially at higher levels and without the use of items, training for four hours in the hall is worth more experience. And unlike when it was released, it is affordable enough to be useable. (I think it used to cost 20s per exp! Now it's something like 8s)
Being able to restore them to full energy once a day helps too, cheaper in the long run than energy potions and reliably there.

I do like to have the pets I am training available to explore but will set them all up to train before I go to bed at night. If I have the silver.

Finally, if you find energy potions, hoard them! wait until you have a good scroll that grants bonus EXP and try to make the most out of that scroll.

Thank you very much for the tips and advises :) I'll start to save silvers for a ridinghall and the sanctuary, and keep training on islands against monsters n_n 

If you are onlyne diary, aprox how long does it takes to ahve a pet at the lvl 50?

It depends on a few things, how many battles the pet wins and how much exploring you do mainly. Genes have a pretty big impact on that.

With the sanctuary towards level 35ish and no items I got Hadassah to level 50 in around 18 days. This is without a ridinghall he could use.
Daria, my other starter I still have, has spent 2 days pregnant but and due to her worse genes is only level 35, without sanctuary but she has been trained in the hall for at least 5 levels.
Sinderion is around 4 days younger than Hadassah, so he's had about the same training as Daria and he's level 46. He should hit 50 tomorrow. (With only a couple levels gained in the hall and no sanctuary until the last couple days.)

People who used lots of items, energy potions and scrolls, were able to get their pets to level 50 in around a week I think?

My first level 50 unicorn was Andromeda ( http://beastkeeper.com/pet/4508 ), I got her to level 50 by the 3rd of March, but that was using a couple of major scrolls of insight and alot of energy potions and my sanctuary.

Perseus ( http://beastkeeper.com/pet/19102 ) finished taming on the 9th of March, and I had him up to level 50 by the 13th of March, using the same method as I did for Andromeda.

Athena ( http://beastkeeper.com/pet/18445 ) matured on the 10th of March, and I got her to level 50 yesterday with 1 major scroll of insight, and far too many energy potions. 

But all 3 of these have good genes/stats which made levelling them easier, on the other hand, Kato ( http://beastkeeper.com/pet/8625 ) doesn't do so well, i had used some scrolls on him, and several energy potions, but he just doesn't do as well against island mobs, so I gave up on trying to rush level him, and just decided to take it as it comes......he will get there eventually, but is currently level 41

Just got on a few days ago, wanted to ask if Strength & other stats increase with battling or if they just stay the same? Also where can I go to find a list of the moves/countermoves in battles, I didn't bother to copy them down & now when I want/need them I can't find them. Thanks.

^Stats increase with every level-up. Which ones get improved the most depends on your pet's diet.

As for countermoves:

Blow counters Bite

Rush counters Blow

Bite counters Rush