Ok, so I started out as a summoner and boy are they fun, but there are some key factors to remember. Firstly and foremost. The summoner class is not made for close range battle (DUH) secondly, the first skill in the game, is your best friend.
From lvl 1-20 put all skill points in soul blast, this will prove, very, very effective in defeating enemies, considering you'll be doing heavy damage which will destroy enemies around your level (give or take 3-5 levels) in 1-2 shots. The summoner is a rather fast class to level, and is a useful character in parties.
There are several ways you can build up your summoner statwise, the first way is the most obvious.
Pour into INT all stat points for 8-10 levels so you have a lot of SP to drain, keep in mind your going to have to dodge enemies and stay away from big mobs that can pwn you in a couple shots.
Another way is a more balanced and evened out stat build which would require more patience but a more stable leveling pattern. This is where you up stats in a sequence pattern, 4 into int, 1 into vit in the first level, 1 into int 2 into dex and 2 into vit, next level, and so on. Dex will increase your accuracy (not that you need it) and avoidibility (definitely need it) You'll be draining your SP faster with the use of higher level soulblasts, but won't be getting hit by pesky mobs as much.
If you go the first route, after you hit about lvl 8-11, start evening out your points, 3 int 2 vit, vice versa, and slowly add into dex. At lvl 20 you start getting 6 stat points, which is good, now you can even out some more, but once you get to 1,000-1,500 sp I would slow down with the int and focus on dex, vit and ego, ego is going to be very useful for the bloody summoner as you get even higher.
Ok, so now you got your summoner mastery to lvl 20, and you just leveled up, meaning you can start making Elementals, WOOPIE!
Your first choice is your green elemental, take it NAO!
A little advice with summons, to select your summon, hold shift and drag a box around it now that its selected hold ctrl and click a enemy, and bam it'll attack. The summon will automatically attack and cast spells when your being hit,
note: not being attacked, only when your hit.
The green elemental will seem useless in the beginning, but its quite good, its ugly, but good. Firstly his AoE and his taunt, he will taunt all monsters around and pretty much tank the damage allowing you to choose which to pick off, secondly, as he levels up, he will learn sleep and become much much more powerful. He evolves around lvl 13 and again as 25 (max skill level) I do not advise just focusing on one element. Also, the green element increases your SP recovery rate, but his ASPD (attack speed) is rather slow.
At summon mastery lvl 25, you'll acquire the ability to choose another summon. This is totally up to you, but I'll explain the routes you can take.
The blue element, is awesome, with all the spells this mad element can learn leveling becomes extremely fast, basically its like summoning your own pocket sorceress, she'll pretty much be tanking most of the damage because of how fast she casts and pisses mobs off, as she levels up, she turns into a devastator of worlds, its amazing how good she gets. If you go with her, for the next 5-10 levels pour into her before your green element, seeing how he'll be more supportive and she'll be tanking.
The Red element is a monster, and is definitely the best looking summon, at max level he's a pocket demon, he is IMO the best one to take on boss monsters and amazing in PVP with his close range powerful attacks. Once again, either focus strictly on him for a while and slowly pour into the green or do them semi-evenly, 3 levels to red, 1 to green.
Depending on your preference, you basically choose which direction you want your summons to work in. Either 1 close range and 1 supportive with you to kick in those heavy damaging soul blasts or 1 supportive and 2 magically casters (you and the blue element)
Now theres the alternative and more avoided routes some players take because, well...they can be pretty effective. There is the 3 summon monstrosity (I made that name up

) anywho, basically, its evenly leveling up all 3 summons at the same time, why is this harder? well because generally you'll have 3 weaker summons instead of 2 strong summons, but it starts to pay off, with 3 summons its like a wall of death, always being attacked by something and everything. The con about that is, you won't be able to pour more skill into summon upgrades and boosts while your focusing leveling up all 3 equally. You can tweak this out to still have all 3 but different levels depending on preference.
The next, is the BME (big motha elemental) basically focusing on 1 element to the point where its stronger then you, by pouring all the skills into that elemental and then pouring the rest into the upgrades and buffs for the element you have a dominator. If your going to do this, go red or blue, stay away from green.
Now heed my words, if your making a summoner, do not put any skills into confuse or tame (my mistake, I had to restart my summoner) why is this? because your green one gets confuse and their just a waste of a skill, your going to be focusing more on handing up damage then nap time.
Pick up every, and I mean, every item you see, all the potions, cases and kar, upgrade your lvl 2 gears, try to do a quest with every NPC in every town you visit. Complete every quest you get (good exp, good kar, and items in some cases) try to stay away from tunnels if your a low level, unless you like to journey and you got portals.
Your base stats for a summoner are
EGO 15
STR 10
DEX 10
INT 25
VIT 25
If you go with the first stat build up method, you should have roughly this by level 20.
EGO 15
STR 10
DEX 10
INT 95
VIT 50
If you go more balanced you should have by level 20.
EGO 15
STR 10
DEX 15 - 25
INT 75 - 85
VIT 35 - 45
Remember stop pouring into INT once you get to about 1k and start focusing a little more on vit, dex, and ego, if you have to STR because of weight limit and what not, but not to much.
Remember, I ain't no pro (yet) but thats where your stats should be roughly.